#### Back to index | # Info for ti99_4a

#### Texas Instruments TI-99/4a Home Computer

Known Issues:
Requires full keyboard emulation. At startup, full keyboard emulation mode is
enabled by default. Whilst in full keyboard emulation mode, some key
associated functionality may be disabled (like the ESC key for EXIT).
The keyboard emulation mode is toggled using the scroll_lock key.

Usage:
This TI-99/4a driver offers a high level of compatibility, and implements

several optional extensions:
* Image cartridges are in V9t9 format (see below for instructions).
* Speech synthesis is emulated completely. The speech synthesizer occasionally
generates some weird noises instead of the expected phonemes. I think the
actual reason for this issue is the original ti-99/4(a) speech synthesizer did
not use the tms5220 chip that is used under emulation: I think I have read
somewhere that TI 99/8, which did use a tms5220, was affected by similar bugs.
* Three types of memory expansion cards are emulated: the original TI 32kbyte
card, and the Super AMS card, and the Foundation card.
* Any of three different floppy disk controllers can be emulated: TI's original
SD disk controller, SNUG's BwG disk controller, and Myarc's HFDC disk
controller. Note that neither the hard disk nor tape interface of the HFDC
card are emulated. These disk controllers have different abilities: TI's
controller only supports single density disks with 9 sectors per track and 40
tracks per sides; the BwG controller supports double density, and it uses no
VDP RAM at all; the HFDC controller supports 80-track disks as well (high
density support is incomplete and non-functional because of TI99 bugs). Four
floppy disk drives are emulated, but the TI controller only supports three of
them (the fourth disk drive will be ignored if the TI controller is selected).
Floppy disk images are in a MESS-specific format that is compatible with
single-sided V9T9 disk images (but not double-sided ones).
* Thierry Nouspickel's IDE card prototype is emulated. A description can be
found on Thierry's page along with the required disk-based DSR. Note that
there are two minor errors in the DSR disk image: the byte at offset >12 must
be edited from >02 to >01, and the byte at offset >7601 must be edited from >21
to >20; the byte at offset >13 should be edited from >02 to >01, too, but this
is not a critical issue at present. Note that the disk image does not work
very well with the BwG disk controller, though I cannot figure out why (it
works fine with both the TI controller and the HFDC controller). The hard disk
image is a standard MAME disk image; since MESS does not support image diff
file currently, only un-compressed images can be written to (compressed images
ARE supported, but only as read-only disks).
* Serial port and PIO emulation is incomplete. On the one hand, nothing useful
can be done with the RS232 interface, but, on the other hand, the PIO interface
enables you to redirect PIO output to a file and save listings to this file by
"printing" them to PIO.
* SNUG's HSGPL support is incomplete, but you can already play with it if you
want to. You will need the HSGPL DSR (and probably the software manual, too)
from the SNUG web site to do anything useful. The FEEPROM is saved to a file

called "hsgpl.mem", in the memcard folder. Its format is relatively simple:
byte 0 is always 0, and the rest of the file is made of four similar sections
for each Flash EEPROM (DSR, GROM0, GROM1, and ROM6); the first byte of each
section is 0, the second should be 1, and the next 512kbytes is the raw FEEPROM
data. The DSR and system GROM0 needs to be loaded into the FEEPROM: to do so,
you can use a hex editor to create a hsgpl.mem file in correct format.
Afterwards, you may write extra GROM using the HSGPL DSR. Note that Supercart
and MBX paging are not emulated correctly, and there must be other issues.
* The tape interface is emulated. The CS1 unit is read/write, whereas CS2 is
write-only. Tapes are stored as sampled wave files. You may find that the
emulated tape interface is a relatively simple way to exchange files with
real-world TI99s.

Loading a cartridge:
You do not need a cartridge image to run the computer, since TI99/4a has
a small built-in basic interpreter.
V9t9-format cart images are typically split into up to 3 files. You MUST load
all individual files. Loading a single zip archive containing all the
cartridge files will NOT work, you must uncompress the archive and select every
file instead. These files can be loaded in any order, as long as all necessary
files are loaded.

The following file name extensions are recognized for cartridges dumps:
* "g.bin", ".grom" or ".g": GROM dump
* "c.bin", ".crom" or ".c": CPU ROM dump
* "d.bin", ".drom" or ".d": CPU ROM dump for second page (pages cartridges
only), to be loaded alongside a CPU ROM dump
The following two types are supported as alternatives to the CPU ROM type

(these extensions are only found in MESS, not V9T9):
* "m.bin", ".mrom" or ".m": minimemory CPU ROM dump; similar to CPU ROM dump,
but the address range >7000->7fff is set up as RAM (paging is not
supporting); unfortunately, there is no way you can save the contents of
minimemory to disk
* "b.bin", ".brom" or ".b": MBX CPU ROM dump; similar to CPU ROM dump, but the
address range >6c00->6ffd is set up as RAM, and the paging scheme is
different; unfortunately, I do not have any correct dump of a MBX cart to
test emulation with

Setting up the system configuration:
A few dip switches enable or disable computer extensions. These switches are
only read at reset. Therefore, if you edit them, you must reset the emulator
(press F3 in partial keyboard emulation mode) for the changes to be taken
into account.

History and Trivia:
The TI-99/4a Home Computer was a TI-99/4 with improved keyboard, revised
ROMs, and an additional graphics mode. It was officially introduced in
June 1981, and was retired in late 1983.
TI99/4a was quite successful in Europe and US (possibly hundreds of
thousand units built). In 1983, though, competition on the home computer
market was so harsh that TI had to cut down the price of TI99/4a to less
than $100, while suffering heavy losses. So, by the end of 1983, TI had
abandoned TI99/4a, its prototype successors, and withdrawn from the home
computer market.

created on Mon May 19 14:44:27 2003