EEPROM loader & manager for the USB-SM card

This page describes ELM ("EEPROM Loader & Manager"), a program meant to manage the EEPROM on the USB-SM card. Its main function is to load new DSRs into the EEPROM, but it also lets you inspect the EEPROM, edit it, and possibly remove old DSR.

There are 3 level at wich the progem can be used:

  1. As a DSR loader, to load a single DF80 file.
  2. As an EEPROM manager, to enter commands and view their results.
  3. Or you can feed it a script file, in DV80 format, containing a pre-arranged series of commands and/or files to be loaded.

The distibution disk can be downloaded here (zip file, 58K), in disk-image format, i.e. a sector dump in numerical order. To transfer it to your TI-99/4A, see my download page.

The disk contains the following files:

ELM/1 to ELM/7     Prog   EEPROM manager and loader
MENU DV80 Menu driven interface for ELM
MENU_B, MENU_E DV80 Submenus called by the above
STDMEM/O DF80 Standard memory access routines
USBHOST/O DF80 Demo DSR, to access USB devices from Basic
USBHOST DV80 Script loading the above two files
DIRECT Prog Basic demo program
GEDESC Prog Basic demo program
HOST Prog Basic demo program
INTS Prog Basic demo program
PORTS Prog Basic demo program

Loading a new DSR
Command mode
Demo DSR

Loading new DSRs

This is the simplest way to use the EEPROM manager. Before you start, make sure that all switches on your USB-SM card are in the proper position: the one on the back should be all the way back with a TI-99/4A or in the middle position for a Geneve. The switch in the middle of the board should be forward with a TI-99/4A, and to the back with a Geneve. In addition, you should close the top switch (labelled EE) on the DIP-switch located to the front of the board. This will unprotect the EEPROM and allow the program to write DSR into it. You may want to open this switch once you are done: this will prevent any malicious program (e.g. a virus) to install itself permanently in your USB-SM card.

Load the file ELM/1 with a EA5 loader such as Funelweb, the Editor/Assembler cartridge option 5, or the TI-writer cartridge option 3.

The program automatically scans for the USB-SM card and displays its CRU address and the size of its EEPROM.

At this point, just type in the name of the file you wish to load. In most cases, it will be a DF80 file, but it could also be a DV80 script file.

The program then prescan the file and displays its info screen, if it contains one. Press any key to continue with loading the DSRs, or press Fctn-= (QUIT) if you realize this is not the file you wanted. If the file does not contain any information for the user, you don't have the option to abort loading. Neither do you when you are running a script, unless the author of the script chose to give you such an option.


If you have more than one USB-SM card, several CRU addresses will be displayed. The last one will be used by default. If that's not the one you want, type in "CRU 1x00", where x is the address you want.

If the USB-SM card is not found, most probably the main switch was left in the "off" position (or the TI/Geneve switch is wrong). Correct the problem then type in "CRU" to repeat scanning. Or just restart the program.

Command mode

Load the file EEMAN1 with an EA5 loader. You then have two possibilities:

If you prefer a menu-driven interface, type in DSK1.MENU (or whatever drive the files MENU, MENU_E, MENU_B are located in). This will launch a chain of scripts that let you access most (but not all) commands through a series of menus. The script files are in DF80 format and can thus be read with a text editor. If you need examples of how to use commands, you may want to take a look at these files.

If you like a command line interface better, just type in commands, in upper-case. Many commands can be abbreviated by just typing their first two letters (see command summary). The following function keys are active: Fctn-3 erases the line, Fctn-S backspaces.

Commands can be divided into several groups: file-oriented commands, EEPROM-oriented commands, debugging commands, and script-file commands. A command summary is provided at the end of this chapter.

Most commands produce screen output, so you know they are executed correctly, but there are a few silent commands. As long as you don't get an error message, you can assume that the command was executed properly.

If an error occurs, you may have the option to ignore it and continue with the command, at your own risks. This is not possible with every command, though. If you are executing a script, you are also given the option to abort the script and return to command mode. Errors that report duplicate names (e.g. duplicate DEF, or duplicate DSR or call) give you the option to replace the old entry with the new one, or to keep the old one and just ignore the new one.

To exit the program from the command line interface, just type EXIT

Entering numeric values

Many commands take numeric values as parameters. All numeric values are assumed to be in hexadecimal format, so there is no need for the > mark, although it is accepted. If you wish to enter a decimal number, you must precede it with a # sign. In other words, #10 means ten, whereas >10 and 10 both mean sixteen.

Wherever a numeric value is required, you can substitue a symbol name preceded with an @ at sign (e.g. @TEST). The value of this symbol will be used, if is is found in the symbol table. If the symbol is not found, the value is zero by default. Several internal variables used by the loader can be accessed in this way, see table below. (In some cases, you can also use labels where a text value is required, in wich case the label should contain a pointer to a string).

You can combine numeric values and symbols in mathematical expressions, using the following operators:

Unary operators, act upon the value that follows:
+ ignored
- negation (-1 is FFFF)
~ bitwise inversion (~1 is FFFE)
` absolute value (this is the "accent grave": Fctn-C)

Dual operators, combine two values:
+ addition
- substraction
* multiplication
/ division
% modulo (remainder of division)
] the greatest of two (signed comparison)
[ the smallest of two (signed comparison)
& bitwise "and"
| bitwise "or"
^ bitwise "exclusive or"

Unary operations are performed first. Dual operations are performed in order of appearance. To alter the order of execution you can use parentheses ( ) , which can be nested upto 5 levels deep. Parentheses mismatch or overnesting abort the calculations. As a general rule, any syntax error aborts calculations and returns the current value, calculated upto the point where the error occured. Note that no check is performed for carry, borrow, nor overflow during arithmetic operations.


File loading commands

These commands are used to load DSRs from object files and "burn" them (i.e. write them) into the EEPROM.


LOAD command

This command causes a DF80 tagged-object file to be pre-scanned. The loader looks for the segment structure within the file (tags M) which it uses to build the segment table, and for DEFs and REFs which it places into the symbol table (unless a DEF has the same name than a segment, in which case it is assumed to contain segment flags for the segment table).

Once it is done reading the file, the loader calls its dispatcher routine and attempts to assign each segment to a page within the EEPROM.

If everything goes well, you are now ready to burn segments into the EEPROM, or to review file contents with commands like INFO, EXPORTED, or ENTRIES.

The LOAD command can also be used to trigger execution of a DV80 script file, or to chain script files if enclosed within a script (note that there is no mechanism to return to the same point in the calling file once the chained file is finished).

Normally, the command should be followed with a file path, i.e. a drive name and a file name: DSK2.MYFILE. But there are several alternative syntaxes. If the file path begins with a decimal point, the default path name (DSK1.) will be substituted for the dot. If the path begins with DSK*, the number of the most recently used drive will be substituted for the star. Finally, you could use a label pointing to a string, which should contain the file path (e.g. LOAD @_PTR).

BURN command


This command causes the DF80 file to be read again, once for each segment, starting from the end of the file. The segments are assembled one by one into the memory expansion card, then written into the EEPROM (a.k.a. "burned", a term that dates from the time PROMs were made of tiny fuses that were burnt to write a '0' bit).

BURN segment_number
BURN "segment_name"

Alternatively, you can use the command to write only one segment into the EEPROM, by specifying either its number or its name enclosed in doubled quotes. Note that the loader will need to assemble in RAM all segments following the one you're burning, for proper resolution of the REF chains. So if you're planning to BURN more than one segment, it is best to burn them in reverse order of appearance in the file (i.e. start with the last one).

RESET command


This command wipes out the segment table, the symbol table and restores several values to their default. It is approximately similar to exiting the program and restarting it, except that you don't loose the CRU address, nor some of the debugging settings.

If you wish to load more than one DSR unit in one session, make sure you insert a RESET after each unit has been burnt.

There is a special syntax of this command:


which only resets segment-related info, but preserves the symbol table.

INFO command

This command is used to display the information segment in the DF80 file, if there is one. This segment will never be loaded, it is only meant to provide information about the contents of the DSRs.

There are 4 records in this segment: a target identifier (which should say USB-SM), an info line, an info screen, and a custom info field.

If the info segment contains a screenful of info, it is displayed until you press a key. Then the target name and the info line (if any) are displayed and the command ends.

ENTRIES command

This commands loads the blank (no-name) segment from the DF80 file, and displays how many of each entry points it contains: DSRs, CALLs, power-up and interrupt service routines. It also verifies that there is enough room in page 0 to load this segment.

DSRs: 0002    Calls: 0001
Pwr-up: none ISR: none
Will not fit in page 0

To get detailed information on the entries about to be created, you can follow the command with a parameter: DSR, CALL, ISR, POWERUP, or ALL (only the first letter is scanned). The relevant entries are listed with the following format:

? Name    Addr Dup
- ------ ---- ---
D OTHER 4132
C CALL4 4144
p 4160
i 415E
Will not fit in page 0

Since the entry segment is generally burned last, it is a good idea to call this command before calling BURN, in order to detect potential problems before anything is commited to the EEPROM.

After execution of an ENTRIES command comprising a parameter, _ITEMS will contain the number of items listed. ENTRIES without parameters sets _ITEMS as zero.

EXPORTED command

This command loads the EXPORT segment from the DF80 file (if any) and displays it on screen. It also checks the exports list whithin the EEPROM and makes sure there are no duplicate names.

Name   Addr Dup Segment Page
------ ---- --- ------- ----

After execution, _ITEMS will contain the number of exports found in the EXPORT segment.

EXIT command

This command simply exits the program and resets the TI-99/4A. Whatever EEPROM page that was selected last will appear in the EEPROM. For your DSRs to work properly, this should be page 0 (or the one you substituted for it with the PAGE0 command). To force page 0 selection, just turn the console power off, then on.

Analyzing the EEPROM

There are several commands dedicated to the analysis of the data currently within the EEPROM.


VIEW command

This is the most basic command: it just displays the contents of the EEPROM. There are several syntaxes:

VIEW address:page

This version of the command displays 128 bytes of data, arranged as 16 lines of 8 bytes.

VIEW 4000:1
4000 50 00 00 01 4D 41 4C 4C
4008 4F 43 41 80 00 03 46 52
4010 45 45 20 20 41 84 00 03
4018 52 41 4D 43 50 59 41 88

Address is the address where the display should start. Normally, it will be in the range >4000-5FFF, but this is no obligation: you can use VIEW to display any cpu memory area.

Page is the number of the EEPROM page, if address is within >4000 to >4FFF. Otherwise, it is assumed to be the number of the SRAM page (the SRAM maps at >5000-5FFF). The maximum number of EEPROM pages is displayed when starting the program: it's either >0800 for an 8 meg EEPROM, or >0400 for a 4 meg EEPROM. The maximum number of SRAM pages is >0100.

VIEW address:page,ASCII

This is the same as above, but the presence of the ASCII flag (only letter A is checked for) turns the display into text. There will still be only 8 bytes per line, at the same positions as the hexadecimal bytes were, so you can figure out more easily which is which. Unprintable characters are displayed as double underscore, which lets you differentiate them from the regulr underscore character (ascii 95) which appears only once.

VIEW 4000:1,A
4000  P  `  `  `  M  A  L  L
4008 O C A ` ` ` F R
4010 E E A ` ` `
4018 R A M C P Y A `

VIEW address

This displays another address from the same page, in hexadecimal or ascii, depending on what was the case the last time the command was typed in.


This diplays the next 128 bytes, in the same format as previously


The displays the previous 128 bytes.

After execution, _PAGE contains the number of the displayed page, and _PTR the starting address of the displayed memory.

PAGE command

This command lets you analyse EEPROM pages. It works best if pages in use contain the default link structure installed by the loader, in which each segment is preceded with a pointer to the next segment. However, it can also provide information about non-standard pages.

There are 3 disting syntaxes, differing by the number of parameters. The simpler version, PAGE with no parameters, displays a summary of EEPROM pages:

Free: 07F8  Bytes: 7F98A6
Used: 0008 Segments: 000C
Content Page Items Free
------- ---- ----- ----
Exports 0001 000B 0FE8
Units 0002 0003 0F7E

Free is the number of free pages, followed with the number of free bytes. Each free page contributes >1000 bytes to the total, to which the program adds any free bytes remaining at the end of used pages. Note that, due to time constraints, the program does not actually verifies that all 'free' bytes contain >FF, it just trusts the link structure installed in used pages.

Used is the number of pages in use, either fully or in part. Segments indicates how many segments are loaded into these pages. This number includes all stubs, so it may be greater that what is displayed with the UNIT command.

Then the program lists all export pages and all "unit" pages, i.e. those containing removal information. For each page, its number is displayed together with the number of exports or units in the page, and the remaining free bytes at the end of the page.

After execution, _ITEMS contains the number of free pages. _PAGE contains the number of the first units page.

PAGE first,last,flag

You can get a more detailed listing by following the command with a range of pages.

First is the first page to be listed.
Last is the last page included into the listing.
Flag is an optional condition: if it is USED (or just the letter U) only used pages will be listed. If it is any other value (such as FREE) only free pages will be listed. If it is omitted, all pages will be listed.

PAGE 0,6
Page  Segs  Used Blank
---- ---- ---- -----
0000: 0000 0000 Blank
0001: 0001 1000 0EB2
0002: 0001 1000 0FA8
0003: 0003 0C32 05C4
0004: 0002 06D8 0B1E
0005: 0000 0000 Blank
0006: 0000 0000 Blank

After execution, _ITEMS contains the total number of pages listed, i.e. matching the flag, _PAGE contains the number of the last page listed.

PAGE number

To get even more details on the contents of a page, you can use the PAGE command with a single argument, the page number. The following type of listing is produced:

Addr Size
---- ----
4000 017E Default stub
417E 055A
46D8 0558
4C30 03D0 Blank

The first segment in a page is systematically compared with the default stub used by the loader. If it is identical, this will be indicated in the third column. If it matches the default stub but uses more space, stub extensions were included, which is indicated by a '+' sign.

After the last segment, one more line is printed with the number of blank bytes (i.e. containing >FF) at the end of the page. If the last segment finishes with >FF bytes, they will be included in the count, so the number of blanks may be greater than expected. If the last segment reserved the full page, the number of blank bytes at the end of the page will be indicated on the segment line.

Addr Size
---- ----
4000 1000 Blank: 0EB2

If a segment was loaded without using the default chaining mechanism (i.e. preceding it with a pointer to the next segment), its size cannot be calculated and "no link" is indicated instead. Since the next segment cannot be found either, the routine just displays the number of blank bytes at the end of the page.

Addr Size
---- ----
4000 No link Blank: 0002

After execution, _ITEMS contains the number of segments listed. This includes the strub segment, but not the blank portion at the end of the page.

HEADER command

This command analyses the EEPROM header to be found in page 0. It expects byte >4000 to be >AA, and further checks address >4010 to know whether the current header is the default one, installed by the loader.

It then analyses the header and displays the following statistics: number of DSR names, number of subprogram (i.e. CALL) names, number of power-up and interrupt routines. If the header is the default one, power-up and ISRs are broken into two categories: the master routine is the one called by the console ROMs, the subroutines are called by the master. Normally, there will be only one master routine in each category, since the loader only installs subroutines.

If the header is the default one, the command also displays the location of the first exports page, and that of the first "units"
page, i.e. the page containing removal informations. Finally, it also displays the number of entry segments in page 0, normally at least one since the default page 0 stub is counted as one.

DSRs: 0003 Calls: 0002
Master PwrUp: 0001 Sub: 0000
Master ISR: 0001 Sub: 0000
Exports page: 0001 Units: 0002
Entry segments: 0002

After execution, _ITEMS contains the number of entry segments found. _PTR points to the first free address in page 0.

You can further refine the analysis, by including after the command the category that you want to be detailed: DSRs, CALLs, ISRs, Power-ups. Only the first letter is checked, so feel free to abbreviate these as D, C, I and P.

Name   Addr Unit (Hex name)
------ ---- ---- ---------
YDSR 4120 0001 05005944
MYDSR 4340 0002
6000 0000

In the exemple above, the first DSR was scratched, by zeroing the first byte in its name. Most probably because unit 2 wanted to define a DSR of its own, with the same name. >05 is the name size, >00 the erased character, >59 and >44 the next two characters ("YD").

There is always an extra entry at the end of the list, don't worry about it. It is a dummy name residing at >4FFE, which allows the loader to extend the chain of names when new DSRs are loaded (>4FFE can be transformed to any address by changing zeros ro ones).

The listing for calls, obtained with HEADER CALL, follows the same format.

However, ISRs and power-ups have no name, so their listing is a bit differnent.

T Addr Unit
- ---- ----
M 4020
i 4192 0001
i 41AC 0002

The listing is identical with HEADER PWRUP which lists power-up routines.

After execution, _ITEMS contains the total number of items displayed.

UNIT command

This command lets you inspect what DSRs where previously loaded into the EEPROM. Each time it installs a new DSR, the loader saves some information about it into a dedicated page(s). This information will come handy in case you need to remove a DSR. Each loading session contributes an entry into this page, hereafter known as a "unit".

By typing the UNIT command without any parameter, you get a summary table of all registered units.

Unit  Seg  Exp  Ref  Entry
---- ---- ---- ---- -----
0001: 0001 0000 0000 Y
0002- 0002 000B 0000 n
0003: 0006 0000 0007 n

After execution, _ITEMS contains the number of units listed. _PAGE contains the number of the last page with unit information in it, and _PTR points to the last unit entry in this page.

UNIT number

You can get more details about a unit by typing its number after the command. The command displays a series of tables, inasmuch as they are relevant for the unit in question:

If you do not wish to see all this information, you can display only one of these lists by typing its name (the first character is enough) after the unit number.

Page Addr Size
---- ---- ----
FFFF 5040 0000
0000 0000 0000
0003 4148 0558

Note that the first two segments are always listed even if empty: the data segment (located in the SRAM, so the page # is irrelevant) and the "no-name" entry segment.

Name   Addr Page Unit
------ ---- ---- ----
MALLOC 4180 0003
FREE 4184 0003
RAMCPY 4188 0003
Name   Addr Page Unit
------ ---- ---- ----
ATSLOT 4194 0003 0001
TOSLOT 4190 0003 0001
MALLOC 4180 0003 0001
FREE 4184 0003 0001
Name   Addr Unit (Hex name)
------ ---- ---- ---------
MYDSR 4340

The display for UNIT n,CALL is identical

T Addr Unit
- ---- ----
i 4192 0001
i 41AC 0002

The listing is identical with UNIT n,PWRUP which lists power-up routines.

After execution, _ITEMS contains the total number of items displayed. _PAGE contains the number of the information page where this unit is listed, _PTR the address of the unit entry in this page.

EXPORTS command

This command displays the exported symbols stored within the EEPROM, if any.

EXPORTS first,total

First specifies the number of the first export to display, counting from zero. If ommited, the default is zero.
Total specifies the total number of exports to list. If ommited, the list is processed upto its end.

Name   Addr Page Unit
------ ---- ---- ----
MALLOC 4180 0003 0001
FREE 4184 0003 0001
RAMCPY 4188 0003 0001

After execution, _ITEMS contains the total number of exports that were displayed. _PAGE contains the number of the page in which the last listed export is located, and _PTR points just after this export entry.

ERASE command

This command is used to erase the EEPROM, i.e. to reset all bytes to >FF, which will allow you to load new DSRs afresh. Erasure occurs by blocks of 128 pages, so you have the option to erase only one block, or the whole chip.

To erase one block, follow the command with the number of any page within this block:

ERASE 21 ; erases pages 32 to 63 (>21 hex is 33 decimal)

To erase the whole chip, just type:


Be aware that a whole-chip erase takes almost a minute to complete.

After the command is completed, _ITEMS contains the number of blocks erased.

PATCH command

With this command, you can modify the content of the EEPROM. But remember that you can only change '1' bits into '0', not the opposite (for this you would need to erase the EEPROM).

PATCH address:page,byte,(byte,...,byte)

The command is followed with an address and an EEPROM page. The address must be in the range >4000-4FFF, do not use PATCH to edit any other memory area, it will not work.

The page number is followed with one or more bytes to be written into the EEPROM. The upper limit is the maximum number of bytes that you can write in a single input line.

PATCH 4028:2,20,00 ; This writes >2000 at address >4028, in page 2

If everything goes well, you are returned to the command prompt. If an error occurs, it is most likely because the write-protection switch was left open, or because the bytes to write would turn 0s into 1s (e.g if >4028 contains >1234, you can't change the '1' into a '2').

SCRATCH command

This command can be used to remove an entry, an export, or a whole unit from the EEPROM. This is useful if you are planning to load a new version of a DSR, which defines the same names as the old one. Note that the items are not actually removed, but rather the first character in their name is zeroed.

You can scratch DSRs and Calls by name, ISRs and power-up routines by entry address, and exports by name. You can also scratch a whole unit, which sets a flag into the unit information table and scratches all exports and entries that belong to this unit.

The various syntaxes are thus:


Removes the DSR named "THIS", by turning the T into a >00 byte.


Ditto, scratches the call named "MINE".


Scratches the ISR with an entry point at >412E in page 0. This is the address where execution begins, not the address of the entry in the ISR chain. The ISR is scratched by changing its entry word to >0000 (the master ISR knows to ignore such entries). The ISR subroutine itself is not altered.


Ditto, scratches the power-up routine which begins execution at address >4410, by zeroing its address in the power-up subchain.


Scratches all entries and exports for the second unit found in the unit removal info pages. It also sets a flag in the unit's entry that marks it as removed.

Note that category names can be abbreviated upto a single letter: D, C, I, P, E and U.

After scratching a DSR or a call, _PTR points to its entry (i.e. a "next-link" word, followed with the execution address, a size byte for the name, and the name itself), and _PAGE will be zero. The same thing happens after scratching an ISR or a power-up routine, except that these entries have no name. After scratching an export, _PAGE contains the number of the page where this export was found, and _PTR points at its entry (i.e. a 6-character name, followed with an address and a page number). After scratching a unit, _PAGE contains the number of the unit information page, _PTR points at the unit's entry in this page, and _ITEMS contains the total number of exports, DSRs, calls, ISRs, and power-ups that were scratched. If the item to erase was not found, _PTR contains zero.

Debugging commands

The following commands are meant for people who write their own DSRs. They allow you to tweak the contents of the memory and to alter the behaviour of the loader, so you can test your DSRs better.


CRU command

This command is used to change the CRU of the target card. Normally, the CRU is assigned automatically, as the program scans for the USB-SM card upon start up. However, if you have more than one card in your system, you can use this command to select one or the other. The command also queries the EEPROM and displays its size in pages.

CRU >1E00

At any time, you can access the symbol _CRU to find out what's the CRU currently in use, and _LSTPG for the number of the last EEPROM page. You could change _CRU with an EQUATE statment, but then there would be no check for the presence of the EEPROM...

SYMTAB command

This command displays the loader's symbol table. Entries in this table come from the REF and DEF tags included within the DF80 file(s) loaded, and from any symbol you defined with the EQUATE command. Exports are not part of the symbol table.

You can affect the listing by specifying which type of symbol you would like to see: DEF, REF, or UNDEFINED (only the first letter is checked). Symbols defined with EQUATE are considered as DEFs. If you do not specify any filter, all symbols will be listed.

Name   Value Seg Type
------ ---- ---- ----
MYDEF 407C 0002 D
MYREF1 4080 0002 U
MYREF2 4090 0002 R

Note that after a LOAD, all REF labels are still undefined. Only after BURN, will they appear as "R".

After execution, _ITEMS contains the number of symbols that were effectively listed (i.e. matched the required type, if any), and _PTR point to the symbol table. Note that the table grows backwards, toward lower memory addresses.

EQUATE command

This command lets you assign a value to a symbol, creating the symbol if it does not already exist. There are many possible syntaxes.

EQUATE symbol,value:segment

This one assigns a numeric value to the specified symbol:


Optionally, you can also specify the segment number, using a : sign as a separator:


Valid segment numbers are 0 (the default) through 127. Values greater than 256 have special meanings: >8xxx is for unresolved refs, >FFFF for solved REFs, >2400 for GOTO labels, etc.

EQUATE symbol,WORD,address:page

This version of the command will read a word from the specified address (evened out) at the specified page and assign it to the symbol. If the page number is not specified, the current page is used.

EQUATE symbol,BYTE,address:page

This does the same, except that only one byte is read, so the symbol value will always be smaller than 256. The address may be uneven.

EQUATE symbol,SEGMENT,"segment_name"

The double quotes around the segment name are optional. The symbol will contain the number of the segment, if it is found in the symbol tabel. In addition, _PTR will point to the segment entry in the segment table (a 6-char name, followed with page, address, size, flags, and 1 reserved word). If the segment it not found, the symbol value remains unchanged, and _PTR will be zero.

EQUATE symbol,$

This special syntax lets you assign the current location in a script file to a symbol This way you can create labels where to jump within the script file, with a GOTO statement. Obviously, this command only makes sense within a script.

Expressions like $+12 are ignored: anything begining with $ stands for the current script line (or more exactly, the address of this line in the VDP memory).
If you display the symbol table, you will notice that the "segment number" is set as >2400 for this kind of label (>24 is the ascii code for $).

After execution, _PTR points at the symbol entry in the symbol table, which consists in the 6-character symbol name, the symbol value, and the symbol's segment number. The exception is for segment, for which _PTR points at the segment's entry in the segment table.

Tip: to obtain pointers to DSRs, CALLs or EXPORTs, use an IF IN statement, and get the pointer from _PTR.

NEWBLOCK command

With this command you can cause the loader to pick a different block for loading a new file, rather than the block currently in use. This will allow you to erase the newly loaded DSRs, should they prove buggy, without affecting those that already were in the EEPROM. There are two possible syntaxes


This version of the command lets you specify a page number. From now on, the dispatching routine will try to fit segments into this page first, then into the following pages, but will not consider any page before this one. The only exceptions being page 0, used for the entry segment, and the dedicated pages used for exports and units removal info. These can be altered with the PAGE0 command.


When used without a page number, the command will scan the EEPROM for an empty block, i.e. 32 consecutive blank pages starting on a multiple of 32 (but not zero). If it finds one, the first page in the block will be the point where subsequent loading will begin.

After execution, the dedicated symbol _FSTPG will contain the number of the selected page, which is also displayed onscreen. The default upon starting the program is >0003.

PAGE0 command

With this command you can substitute another page for page 0. The loader will place the entry segment into this page, instead of page 0. If you so wish, you can also specify different pages for the export list and the removal information (units) list. This will allow you to test your DSRs without disturbing those that are already in place. It is especially usefull to select a page located within a currently unused block: once you are done, you can just erase the block. This can be done by typing PAGE0 @_FSTPG just after calling the NEWBLOCK command.

The syntax is very simple:

PAGE0 pg0,expg,unitpg

pg0 is the number of the page that you would like to substitute for page 0. The no-name entry segment ($BLANK in the segment table) will be loaded in this page, together with a special stub. If this number is missing, the current page 0 specified in symbol _PAGE0, will be selected.

expg is the number of the first page to be used by the export table, i.e. labels defined by loaded programs. This parameter is optional, as you may elect to keep using the same export table that is currently in use.

unitpg is the number of the first page to be used to store unit removal information, i.e. a description of each program that is loaded into the EEPROM. Again, it is optional and you may choose to keep the current one.

These three pages must be distinct. If either expg or unitpg is the same as pg0, it will be incremented by one. Similarly, if unitpg and expg are identical, unitpg will be incremented.

Be aware that the page numbers for exports and units are saved into the special stub installed in page 0. So, once you have loaded anything in the page 0 of your choice (which automatically installs the stub), you cannot alter expg nor unitpg any longer. But you can alwats pick another pg0, with no preassigned expg nor unitpg yet. The command always displays which pages are to be used for exports and units: if they don't match what you just typed, you'll know it's because their value was preset in page 0.

At any time, you may access the symbols _PAGE0 to find out which is the current page 0, _EXPG for the first exports page, and _UNIPG for the first units page. Please do not modify them directly as no sanity check would be done. Be aware that, if the export list or the unit info table grows really big, another page may be added to the existing one. The number of this page will be written at the end of the previous one, after a >0000 mark.

To properly test your DSR, retype the PAGE0 command (without any number) just before you exit the program. This will ensure that your "dummy" page 0 will be present in memory after the console has rebooted and while it's rebooting (so you can test your power-up routines). Note that if you turn the console off then on the real page 0 will be selected, which is a good thing in case one of your routines would lock-up the computer...

SEGTAB command

This command displays the loader's segment table. Entries in this table come from the segment structure of the DF80 file(s), at least for the segment name, its size and any possible flags. After a file is loaded, a displatcher routine scans the EEPROM and attempts to fit all segments into it. The resulting addresses and page number are placed into the segment table. If you used the LOAD command, nothing is actually written into the EEPROM until you issue the BURN command. If you typed the filename directly, an implicit "load & burn" is executed, so SEGTAB shows you what has already happened.

Name   Page Addr Size Flags
------ ---- ---- ---- ----
$DATA 0000 5040 0140 0000
$BLANK 0000 0000 0000 0000
MYSEG 0005 4682 032E 0000
OTHER 0004 4102 0886 0000

Note that the data segment and the entry segment ( BLANK) are always displayed, even if they are not used.

After this command, _ITEMS will contain the number of segments (including data and blank). _PTR will point to the beginning of the segment table.

ASSIGN command

This command lets you modify the segment table after a LOAD, i.e. determine where a segment will be loaded upon execution of the BURN command.

ASSIGN "segment_name",page,address,size,flags
ASSIGN segment_number,page,address,size,flags

segment_name can be the name of an existing segment or a new name, in which case a new entry will be created in the segment table. The segment name must be enclosed in double quotes. It is the only required parameter, all other values can be left omitted or left blank (i.e. using multiple commas) to preserve existing values, or use default ones.

segment_number provides an alternative syntax to the above, in which you provide the number of the segment, as it appears in the segment table. By definition, the data segment's number is 0, and the blank (entry) segment is number 1. You cannot create new segments with this method, as the name has to be entered one way or another.

page is the page you want the segment to be loaded in. If you change this, you should probably also change the address.

address is the address where the segment will be loaded at. Check segment size to make sure there is room enough in the page.

size is the size of the segment. Normally, there is no reason to modify this.

flags are the segment flags, used to alter the dispatching strategy. Any change to these will only take effect the next time the dispatcher routine is called (e.g. with the DISPATCH command). See my USB DSR page for legal flag values.

After execution, _PTR points at the segment's entry in the segment table, or contains zero if the segment name was not found.


ASSIGN SEG1,7,4F00         ; assign segment "SEG1" to adress >4F00 in page 7
ASSING SEG2, , , ,>0001 ; modify segment "SEG2" flags

DISPATCH command

This command causes the loader to scan the EEPROM and see if it can fit all current segments into it. Nothing is actually loaded, but the segment table is updated accordingly. Because a DISPATCH is automatically executed after each LOAD, there aren't many reasons why you would want to trigger it yourself. But there may be cases when you want to execute a modified version of the command:


Whereas the regular dispatch resets all page assignments and restarts from scratch, the MORE mofidier (only "M" is necessary) causes it to retain any valid page assignments. Only segments with an address of zero will be assigned to a new location.

After execution, _ITEMS contains the number of segments that have been reassigned.


This causes the dispatcher to place segments at the same page and address they were in a previously loaded unit. Since segment names are not saved in units, all segments should appear in the same order now than when the unit was first loaded. In addition, only segments with the same size as before will be assigned their previous locations. After execution, _ITEMS contains the number of segments that were successfully dispatched.

This feature is useful when you are writing your own DSRs and made changes to only one segment: instead of erasing the EEPROM and reloading the whole file, you can just reload the segment you modified. For instance, let's say the previous version you loaded was unit #6, and you subsequently modified segment MYSEG. You could type (or run a script) something like:

ASSIGN MYSEG,0,0 ; this clears assignments for segment MYSEG
DISPATCH MORE ; reassigns MYSEG to a new location
BURNW MYSEG ; burn new version of MYSEG

Notes: The ASSIGN statement is not necessary if the modifications you made resulted in changing the size of MYSEG, since DISPATCH UNIT will only consider segments whose size in the file is the same as it was in the unit.

For your program to work properly, the changes you made should not modify the entry point of any routine that is called from another segment: since these will not be reloaded, they will keep calling the old addresses.

PG4SEG command

This command triggers a verification mechanism for the PG4SEG label. When included in your program as a REF, every occurence of the PG4SEG label will be replaced with the page number for the segment in which the previous address is located. For instance:

       BLWP @SGBL

will replace PG4SEG with the number of the page in which the segment containing MYSUB is to be loaded.

The command allows for two types of verification:

PG4SEG 1 ensures that every PG4SEG is preceded with an address in another segment
PG4SEG 2 ensures that every address refering to another segment is followed with a PG4SEG
PG4SEG 3 combines both of the above
PG4SEG 0 turns verification off.

Type 1 violations are announced individually. The symbol _PTR will contain the address of the "orphan" PG4SEG.
Type 2 violations are announced only once. The symbol _PTR will contain the address of the first offending word, i.e. one that contained a label defined in a different segment, but was not followed with a PG4SEG label.

Script-related commands

The following commands only make sense when included into a script file. A script file is a DV80 text file containing a list of commands, one per line. To launch a script file, just type its name on the command line: it will be loaded into the VDP memory and execution will begin immediately. Alternatively, you can use the LOAD command.

A script can call another script file, but there is no mechanism to automatically return to the caller. In fact, the caller is wiped out of memory when the second script is loaded. Of course, the second script may contain a LOAD command returning to the first file, but script execution will always begin at the top of the file.

Comments can be added at the end of each line, after a ; semicolon. Alternatively, you can have a whole line commented out, if it begins with a semicolon. You can also include empty lines, to make the script easier to read.


ECHO command

There are two ways to use this command: the first one is to use it with an YES/NO switch (only the first letter is scanned). This determines whether the contents of the script file will be displayed on screen while it is processed. The default is NO.

The second way is to follow ECHO with one or more quoted strings to be displayed onscreen. The size of each string should not exceed 28 characters. Optionally, one or more / slash caracters can be added outside of the quote marks, each will cause the display to scroll up one line.

You can also use echo to display the value of a given symbol from the symbol table: just use a @ sign followed with the symbol name (outside the quote marks). The symbol value is displayed as an hexadecimal word, and the segment number is not displayed.


ECHO "Press any key to proceed"
ECHO "Press:" // " 1 to continue" / " 2 to end"
ECHO ////////// ////////// /// ; this clears the screen
ECHO @_PTR ; displays the value of this symbol

GETKEY command

This command scans the keyboard and waits for the user to press a key. When this happens, the ascii code for the key is placed into a symbol called _KEY.

N.B. It's generally a good idea to precede GETKEY with an ECHO statement prompting the user for a key...

GETVALUE command

This command inputs a numeric value from the user and places it in the symbol table, in a symbol called _VALUE. The symbol called _PTR will contain a pointer to the string actually typed in by the user.

N.B. It's generally a good idea to precede GETVALUE with an ECHO statement prompting the user for it.

IF command

This command lets you process sections of the script file only if some condition is met. For instance, if the user presses a key, or if a given export was found, etc.

If the condition is true, the script continues with the next line. If it is not true, the script will be read but not executed until an ELSE, ELSEIF, ORIF or ENDIF is met. You can nest as many IFs as you like, as long as you can keep track of them.

The syntax is:

IF name,operator,value

name is the name of a symbol. If it does not exist, the command is ignored (i.e. true). With the IN (or NIN) operator, name can also be a segment, a DSR, a CALL, or an export. The name doesn't need to be enclosed in double quotes, although these are accepted.

operator is the type of comparison to be performed. Legal operators are:

EQUAL is equal to
GREATER is arithmetically greater than (signed)
SMALLER is arithmetically smaller than (signed)
HIGHER is logically higher than (unsigned)
LOWER is logically lower than (unsigned)
IN is among

All operators can be abbreviated upto one letter, as only the first letter is checked. In addition, each operator can be preceded with the letter N to invert the comparison:. NEQ means "not equal, NG means "not greater than" (i.e. smaller or equal), etc.

value is the value the symbol should have for the IF to be taken. As usual with numeric values, you could specify another symbol preceeded with a @ sign: IF MYSYM,EQU,@OTHER

The exception is the with IN (or NIN) operator: the numeric value is replaced with the category to search for the name. Valid categories are (each can be abbreviated downto one letter):

LABEL searches the symbol table for DEF or EQU symbols.
REF searches the symbol table for solved REF entries.
UNRESOLVED searches it for unresolved REFs.
SEGMENT searches the segment table for a segment with this name.
DSR searches the DSRs in page 0.
CALL searches the CALLs in page 0.
EXPORTS searches the export list in the EEPROM.

After a succesful IN, _PAGE will contain the number of the page the name was found in (zero for symbols) and _PTR will point the the name's entry in this page. If the name was not found, _PTR and _PAGE will be zero.


IF MYDSR,IN,DSR    ;true if a DSR called MYDSR exists in the EEPROM
IF THIS,NIN,EXP ;true if no export called THIS exists in the EEPROM
IF MYLAB,EQU,1234 ;true if symbol MYLAB has a value of >1234

ELSE command

This, as you might expect, serves to reverse the conditional execution of an IF. If the IF was taken, everything included between the corresponding ELSE and the corresponding ENDIF will be read but not executed. If the IF was not true, and thus not executed, the occurence of an ELSE resumes execution of the script.

Note that including an ELSE without a matching IF is allowed. Since execution is "on" by default, a lone ELSE will stop execution until a matching ENDIF is met. The same is true for ELSEIF, ANDIF and ORIF.

ENDIF command

This ends a conditional section, whether defined by an IF or an ELSE. From now on, execution of the script resumes normally (unless the IF-ENDIF was nested inside another, of course).

ELSEIF command

This commands combines and ELSE and an IF: if execution was on, it will now stop. If execution was stopped, the expression will be evaluated and, if it's true, execution will resume. The syntax is identical to a regular IF command.

One use of ELSIF is to separate multiple, mutually exclusive, clauses:

; do something if A=0
; do something else if A > 0
ENDIF ;do nothing if A < 0

ANDIF command

This commands lets you combine several conditional expressions. Its syntax is identical to that of a regular IF. If execution was stopped, it remains stopped. If execution was on, the new statement is evaluated and, if false, execution will stop. In any case, only one ENDIF is required to end conditional execution for both the IF and any subsequent ANDIF.

; executed only if A equals 6, 7, or 8.

ORIF command

This command lets you combine several conditional expressions. Its syntax is identical to that of a regular IF. If execution was on, it remains on. If execution was stopped, the new statement is evaluated and, if true, execution will resume.

; executed if A equals 5 or 8

N.B. You can also use ORIF instead of ELSEIF to separate mutually exclusive clauses.

GOTO command

This command is used to jump to another location within the script file. It is followed with the name of a label that must have been defined with a prior EQUATE $ statement (i.e. you can't jump forward: use an IF instead).

EQUATE HERE,$         ; HERE points to this line
... ; some code
GOTO HERE ; loops back to HERE

Be aware that a RESET in a script wipes out the symbol table and thus forgets about any previously defined label. In such a case, consider using RESET SEGMENTS instead.

STOP command

This command aborts the execution of a script and returns to command mode. It is not necessary to include it at the end of the script, although it won't hurt.

COMMAND command

This command lets the user type in a command and executes it. Then it resumes script execution.

Predefined symbols

The loader contains a number of predefined symbols, which fall in two categories. The first consists in routines defined within the default stub. These can be called from your DSR programs with a simple REF statment. Their usage is detailed in another page.

SGB Branches to a routine in another segment.
SGBL Branch and link to a routine in another segment.
SGRT Return from such a routine.
SGBLWP Branch and load workspace pointer to a routine in another segment.
SGRTWP Return from such a routine.
ATR11 Get data word following a call to SGBL.
ATR14 Get data word following a call to SGBLWP.
SGBLX Branch to a routine in another segment, save return point and page on stack.
SGRTX Return from a routine called in this way.
ATR11X Get data word following a call to SGBLX.
GETDAT Get data from another segment.
RAMPG Select a different SRAM page.

There are also three variables, whose content varies during loading:

MYSLOT Address of a reserved 4-byte slot in SRAM memory.
CURPG Current EEPROM page, where the current segment resides.
PG4SEG Page for the segment which contains the label used in the previous word.

The second category consists in variables internal to the loader. They all begin with an underscore character, which is illegal in assembly, so that there is no chance they will interfere with a label defined in your program. But you can view them with the SYMTAB or ECHO @ commands, modify them with EQUATE, and use them wherever a numeric value is required.

_VALUE Result of the GETVALUE command.
_KEY Result of the GETKEY command.
_PAGE Modified by many commands, page number.
_PTR Modified by many command, pointer to a memory location.
_ITEMS Modified by many commands, number of items listed.
_CRU Current CRU for the USB-SM card.
_FSTPG First EEPROM page where to load DSRs (normally 3).
_LSTPG Last page in the EEPROM.
_PAGE0 Page where to load entry points (normally 0).
_EXPG First page for the list of exports (normally 1).
_UNIPG First page for units removal info (normally 2).
_MAXSZ Maximum size for a segment.

Command summary

Command aka Result
LOAD LD Prescans a DF80 tagged-object file
BURN BU Writes segments into the EEPROM
INFO IN Displays the INFO segment from file
ENTRIES EN Displays the entry segment from file
EXPORTED ED Displays the EXPORT segment from file
RESET . Restores loader's defaults
VIEW V Displays memory
HEADER HE Analyzes EEPROM header
PAGE PG Analyses EEPROM pages
Writes data into the EEPROM
SCRATCH . Removes a DSR, call, export, etc.
UNIT UN Analyzes previously loaded units
EXPORTS EX Displays exports stored in EEPROM
SYMTAB SY Displays the symbol table
EQUATE EQ Add/modify a symbol
SEGTAB SE Displays the segment table
NEWBLOCK . Selects first loading page, in a blank block
ASSIGN AS Modifies a segment entry
DISPATCH . Assigns all segments to EEPROM locations
PAGE0 . Changes page 0 number
PG4SEG . Toggles PG4SEG verification mechanism
ECHO . Turns echo on/off or displays text
GETKEY . Inputs a key from user
GETVALUE . Inputs a numeric value from user
IF . Conditional script execution
ELSE . Reverses conditional execution
ENDIF . Ends conditional execution
ELSEIF . Combines ELSE and IF
ANDIF . Combines two conditional statements
ORIF . Combines two conditional statements
GOTO . Jumps to a label in script file
STOP . Exits script to command mode
COMMAND . Lets user enter a command within a script
EXIT . Exits the program


This demo DSR is meant to let you access USB devices (via the USB host controller) from Basic or Extended Basic.

To load this demo DSR, first launch the EEPROM manager as described above. Then type in DSK1.USBHOST. This will call a script that loads two DSR files: STDMEM/O (the standard memory management routines) and USBHOST/O (the demo DSR itself).

Once done, enter Basic or Extended Basic. Everything is handled through a pseudo-file called USBHOST.

Opening the pseudo-file

First, you should specify which device you want to talk to, by including it in the filename. All devices answer to number zero, so you can detemine how many are connected, and assign a number to each. Once this is done, you can access each device as an independent file, by using the number you assigned to it.


Where nnn is the device number, from 0 to 127. You could actually open the file with any record length, but 255 is more convenient to transfer large chunks of data.

The pseudo-file consists of 5 records, each corresponding to a different operation:

REC 0 sends "SETUP" packets (i.e. commands) to the device.
REC 1 sends "OUT" data packets to the device.
REC 2 sends "IN" packets, i.e. fetches data from the device.
REC 3 controls the two downstream ports at the back of the card.
REC 4 controls interrupts.

The first three records are used to talk to USB devices. Each one must be first written to, then read. No other access to USBHOST should occur in between the write and the read operations.

Writing to a device

Record 0 and 1 are used in the same way, the only different being the packet ID: SETUP vs OUT.

110 PRINT #1, REC 0:A$,endpoint,maxbytes,speed,toggle1
120 INPUT #1, REC 0:err,actbytes,toggle2

A$ is the data you want to send to the device. It may be an empty string, in which case an empty packet will be sent (usefull for acknolewdging an "IN" packet for instance).

endpoint is the endpoint number, from 0 to 15. Each device is guaranteed to have endpoint 0. For the other endpoints you must first check the device configuration (by sending the GetConfigurationDescriptor command via a SETUP packet). If this parameter is ommited or negative, the endpoint most recently used (with any device) will be used again. At power-up time, the default is endpoint zero.

maxbytes is the maximum number of bytes per packet. If this is less than the number of characters in A$, the host controller will split the operation into multiple packets, alternating the toggle bit between 0 and 1 for each of them. If this parameter is ommited or negative, the value most recently used (with any device) will be reused. At power-up time, the default is 8.

speed is the USB transfer speed. Odd numbers select half-speed, even numbers full-speed. If this parameter is ommited or negative, the last speed used with this device will be reused. At power-up time, the default is full-speed. With device 0, the correct speed is automatically determined when opening the file, and used as a default.

toggle is the initial value of the toggle bit used when sending data packets: 0 for DATA0, 1 for DATA1 packet ID. If this parameter is ommited or negative, the most recent value used by this device will be inverted. At power-up time, the default is 1.

actbytes is the actual number of bytes transfered. If it's lower than the size of A$, an error probably occured.

toggle2 is the value of the toggle bit for the last packet that was sent.

err is the error code returned by the controller:

 0: No error
1: CRC error in last data packet from endpoint
2: Bit stuffing violation in last data packet from endpoint
3: DATA0/DATA1 toggle mismatch
4: Endpoint returned a "STALL" PID
5: Device not responding
6: PID check bits mismatch
7: Unexpected PID (illegal value, or legal but at the wrong time)
8: Data overrun, i.e. the endpoint returned more than "max bytes" in a packet, or more than "total bytes".
9: Data underrun. i.e. the endpoint returned less than "total bytes", yet less than "max bytes" (i.e. no more coming).
12: Buffer overrun. During an IN, the host controller received data faster than it could pass them to the system.
13: Buffer underrun. During an OUT, the host controller could not get data from the system fast enough to send them.

Reading from a device

USB being an host-centric system, all transmissions must be initiated by the host. Thus, to read data from a device, you must first query it. This is done via record 2:

130 PRINT #1, REC 2: totbytes,endpoint,maxbytes,speed,toggle1
140 INPUT #1, REC 2: B$,err,actbytes,toggle2

totbytes is the total number of bytes that you are expecting to receive from the device. If this parameter is ommited or negative, the value most recently used (with any device) will be reused.

B$ is a string that will contain the data sent by the device.

All other parameters have been described above.

Controlling the ports

Record 3 is used to control the card ports. It can be read or written to independently. Reading returns the port status, writing controls the port. Let's examine reading first:

200 INPUT #1, REC 3: port1, port2, chg1, chg2, hub

port1 is the status of the bottom port.

port2 is the status of the top port.

The status breaks down to the following bits:

512: low speed device connected     
256: port power is on
16: resetting port
8: overcurrent detected
4: port is suspended
2: port is enabled
1: device connected

chg1 indicates changes to port1 since last time it was read.

chg2 does the same for port2.

 16: reset completed
8: overcurrent bit has changed
4: suspended bit has changed
2: enabled bit has changed
1: connected bt has changed

hub is the global status of the hub controller and breaks down to only two bits:

32768: remote wakeup occured
2: overcurrent detected

AS mentionned above, writing to record 3 controls the ports:

220 PRINT #1, REC 3:set1,set2

set1 sets the bottom port.

set2 sets the top port.

Writing a zero has no effect, which is convenient when you need to set port 2 without affecting port 1. The set word is a combination of the following values:

512: turn power off
256: turn power on
16: reset the port
8: resume suspended port
4: suspend port
2: enable port
1: disable port

Using interrupts

Record 4 is used to control the interruption mechanism: upon certain condition, the DSRs can interrupt your program and branch automatically to a predefined line number. This way, you don't have to constantly monitor the USB controller to know if a device was plugged in, if data came in, etc. Note that the mechanism suffers from a major flaw: Basic statements that do not continue with the next line cannot be interrupted (e.g. GOTO, NEXT, IF, etc). But, hey, this is just a demo DSR...

To setup the interrupt mechanism, write to record 4:

300 PRINT #1, REC 4:mask,line

mask specifies which event you want to trigger an interrupt. It is a combination of the following values:

16384: clock is ready (160-1000 usec after a wakeup).
8192: host controller suspended.
1024: transfer completed (to/from CPU).
512: ATL should be read.
256: ITL should be read.
64: change in port status or hub status.
32: frame number overflow.
16: unrecoverable error.
8: device resuming signal.
4: start-of-frame occured (happens every millisecond!).
1: scheduling overrun.

line is a line number where the interrupt should branch. It must be a REM line, immediately followed with a statement accessing record 4. This second line number should be exactly 10 higher than the REM line. NB: if you resequence you program, you will need to update the value you're setting up.

If mask is negative, special actions are taken depending on the value of line:

  • If line is negative or missing, interrupts are disabled. Basic execution continues normally.
  • If line is zero, interrupts are enabled and Basic execution continues at the point where is was interrupted.
  • If line is positive, interrupts are enabled and Basic execution continues at the line immediately following line.

    To check the current interrupt status, just read record 4:
  • 1000 INPUT #1, REC 4:ints,last

    ints returns the interrupt flags, i.e. lets you know which event has triggered an interrupt. It is a composite of the bit values described for mask.

    last is the number of the last line executed before the interrupt caused the program to jump to the REM line. This may be usefull for you to know what your program was doing before it got interrupted.

    Reading record 4 will also clear the interrupt condition, allowing your program to continue normally.


    100 OPEN #1:"USBHOST.1",INTERNAL,FIXED 255,UPDATE,RELATIVE   ! open device #1
    110 PRINT #1, REC 4:64,790 ! interrupt when port status changes
    120 ... ! more code

    790 REM Interrupt service routine ! This must be a REM line
    800 PRINT #1, REC 4:-1 ! disable interrupts
    810 INPUT #1, REC 4:X ! check status, clear interrupt condition
    820 IF X<>64 THEN ... ! if not our interrupt, do something
    830 ... ! if it is do something else (e.g. check port status)
    890 PRINT #1, REC 4:-1,0 ! enable interrupts, return to interrupted point

    For more examples of how to use USBHOST, check out the following Basic programs:

    GETDESC demonstrates how to get a device descriptor.
    PORTS plays with port status.
    INTS demonstrates interrupts.
    DIRECT demonstrates direct access to the host controller.

    Revision 1. 8/15/04 Ok to release.
    Revision 2. 1/2/04 Several changes. Added demo DSR.
    Revision 3. 1/31/05 Added download instructions.
    Revision 4. 2/6/05 Minor cosmetic changes.

    Previous page (Writing DSRs)

    Back to the TI-99/4A Tech Pages