Texas Instruments TI-99/4A - Successors and Clones

Successors and Clones

At the time they left the home computer market, TI had been actively developing two successors to the TI-99/4A. Neither actually entered production, though several prototypes of each are in the hands of TI-99/4A collectors. Both machines were to feature the TMS9995 CPU and would therefore have been substantially faster than the original TI-99/4A, and both were to use TI's "HexBUS" serial interface (which was available as an option on the TI-99/4A and could be viewed as a prototype for today's ubiquitous USB - the link for the TI-99/8 includes some images of HexBUS peripherals).

• TI-99/2, a low-cost black-and-white only machine with no sound, reminiscent of the ZX81, TS1000 and TRS-80 MC-10 given its 16-bit processor. Designed by Texas Instruments but fairly rare.
• TI-99/8, a premium successor for the TI-99/4A, with a large keyboard, 64 kB of RAM expandable to 15 megabytes, built-in speech synthesis, built-in Pascal operating environment with UCSD Pascal and the full 16-bit data bus available on the expansion port. Designed by Texas Instruments, but abandoned in the Prototype stage. Some prototypes are known to exist and are worth a fair bit of money to collectors. In addition, the emulator MESS is capable of running what are believed to be the system's ROMs.
• Myarc Geneve 9640, an enhanced TI-99/4A clone which was built by Myarc as a card to fit into the TI Peripheral Expansion System and used an IBM PC/XT detached keyboard. Released in 1987, it was in many ways similar to the earlier TI-99/8 which was in prototype form in early 1983. It included a faster processor (12 MHz TMS9995), enhanced graphics with 80 column text mode (via 9938), 16-bit wide RAM, MDOS, and was compatible with nearly all TI software and slot-mounted hardware (an adapter was available to allow the sidecar-only Speech Synthesizer to be installed inside the PEB). A toggle switch was mounted to the side of the PEB to allow insertion of wait states to bring the computer down to the same speed as the original console, allowing compatibility for games and other timing-critical software.
• SGCPU, the Second Generation CPU card was released by the System 99 User Group in 1996 as a card to be installed in the PEB. It was also known as the TI99/4P, and included standard 9900 CPU, ROMs, and up to 1 MiB of 16-bit RAM using the 'AMS' memory expansion scheme. This card required the HSGPL card, which provided the GROM emulation needed to run the system, and the EVPC, which included the 9938 video processor for display.

• The Tomy Tutor and its sibling systems were Japanese computers very similar in architecture and firmware to the 99/8. Unlike the 99/8, it was released commercially, but sold very poorly outside of Japan. Portions of the operating system and BASIC code are similar to the 99/8. According to Barry Boone (a well known programmer for the TI-99/4A), the Tutor's built-in BASIC uses the same internal one byte tokens as does TI's Extended BASIC, and many of the memory scratchpad locations are placed at the same relative locations as the TI-99/4A and TI-99/8. For instance, keyscan values are returned at offset >75 and floating point is stored at >4A.
• The Phoenix G2 Designed in 2010 by Gary Smith a member of TI-User Group UK. This machine uses two FPGAs to emulate the entire architecture of the Myarc Geneve 9640 and the TMS9995 Microprocessor, thus eliminating reliance on obsolete silicon devices. It incorporates the latest advances in technology, such as SD card readers, ethernet, full VGA output, and now 64 MB RAM.