PC99 is a software-only package that emulates the Texas Instruments
TI-99/4A Home Computer and selected TI and third-party peripherals.
Supported PC operating systems:
For other OS support see "Common questions about PC99"
Required hardware:TMS9900 16-bit processor: Fully emulated. All 69 instructions and all corresponding addressing modes are implemented.
TMS9918A Video Display Processor: Fully emulated. Up to 16K VDP memory can be addressed. Supports Graphics I, Graphics II (bitmap), Multicolor, and Text modes (and includes the so-called half-bitmap mode); and sprites.
TMS9901 Programmable Systems Interface: All of the features used on the 99/4A are fully emulated.
TMS9919 Sound Processor: Standard PC: PC99 only emulates TI sound channel 1. This is a PC limitation. PC with Sound Blaster: Fully emulated.
Joystick port: Standard PC: Fully emulated using PC ALT function keys (F1 - F10). PC with game port: Fully emulated.
Command module port: Fully emulated. "Command modules" are DOS files. TI, DataBioTics, MBX, and Mechatronic bank switching schemes are implemented.
GROMs: Up to 16 banks, each containing five 8K GROMs, can be loaded. Multiple GROM banks are emulated using the REVIEW MODULE LIBRARY feature in the TI console.
TI 32K memory expansion card: Fully emulated. This peripheral contains 8K of low memory and 24K of high memory. All of this memory is treated as if it were on the TI fast 16-bit bus.
Myarc 512K memory expansion card: Fully emulated. This peripheral contains 32K of memory which is used as standard TI 32K memory expansion. The rest of the memory can be partitioned into a 128K space for Myarc XB II, and a RAM disk and print spooler.
AMS memory card: Fully emulated. You can select whether to emulate the 128K, 256K, 512K or 1Mb version of the card depending on how much PC memory you have available.
TI disk controller: Fully emulated. The TI disk controller supports up to three drives. Each disk can contain 720 256-byte sectors (DSSD).
Guion disk controller: Fully emulated. The disk controller ROM manufactured by John Guion is included. This allows access to four double-sided single-density drives and the use of "dskn" in lower case.
Myarc disk controller: Fully emulated. The Myarc disk controller supports up to four drives. Each disk can contain 1440 256-byte sectors (DSDD).
TI RS232 primary card: Fully emulated, if the PC has up to two COM ports and one parallel port. PC99 can exchange data at up to 9,600 bps over the PC COMn ports, and can drive a TI compatible printer connected to the PC LPTn port.
Guion RS232 card: Fully emulated, The RS232 ROM manufactured by John Guion is included. This allows access to the "TP" (Thermal Printer) device name.
TI p-Code card: Fully emulated. This card consists of a bank-switched 8K ROM and eight 6K GROMs and lets you run programs developed for the UCSD p-System.
TI Speech Synthesizer: Partially emulated. All of the software functions of the TMS5200 are fully emulated, but no audible speech is generated. This allows you to run programs that require the Speech Synthesizer.
PC99 "card": This is a software only "card", and was not an original TI or third-party peripheral. This "card" contains a DSR for the support of a real-time clock which emulates the CorComp Triple-Tech clock.
PC99 debugger: Displays a TI "Mini-Screen" surrounded by editable objects which allow you to control every aspect of PC99. With the debugger, you can stop any TI application at any time, including during disk access. You can single-step through any TI application, set breakpoints and watchpoints, examine and change any TI addressable memory (CPU, GROM, VDP, and command module space), and read and write the VDP write-only registers.
Multiple ROM banks: Up to 16 64K ROM banks can be enabled. These are switched using the TI bank selection method. This is an extension to the emulation, and allows multiple cartridges with ROM at >6000 to be used simultaneously. This feature also supports cartridges like TI-Calc, which have four switched ROM banks at >6000.
Command modules: TI Extended Basic, Editor/Assembler, Tombstone City and Mechatronic Extended Basic II Plus are included.
Documentation: Supplied on disk. PC99 user manual in Adobe Acrobat pdf format, and txt format for use with an ASCII editor. p-Code introduction, Myarc Disk Manager, Myarc 512K card, Myarc Extended Basic II, and Mechatronic Extended Basic II Plus manuals are in pdf format.
Transfer Utilities: Allow you to move your TI-99/4A Command Modules and disk library to your PC. The utilities transfer binary images of TI disks, in both directions. You need a GRAM device, such as The Gramulator from CaDD (no longer in production), to convert Command Modules to disk format.
Standard Utilities: Allow you to: configure PC99; catalog TI disk files from DOS; extract TI files from TI "disks" and make them DOS files; take extracted TI files and convert them for use in PC programs, such as WordPerfect; and import TI files downloaded from bulletin boards or the World-Wide Web.
There are two PC99 products available: Full and Light. The Full product is the equivalent of:
In addition, you can access the PC99 Mini-Screen debugger. The following table shows the difference in features between each product.
| Program name | PC99.EXE | PC99A.EXE | PC99L.EXE |
| p-System (p-Code card) | Yes | Yes | No |
| 16 GROM banks | Yes | Yes | No |
| PC99 Mini-Screen debugger | Yes | No | No |
| Load interrupt | Yes | No | No |
With either PC99 product you can run TI-99/4A Command Modules and disk-based programs with few limitations. Each product includes files containing all necessary ROMs and GROMs. CaDD is either licensed or has permission from the owners to distribute this copyrighted code.
The minimum recommended machine to run PC99 is a 486 66MHz.