TMS99105 : Kit of ICs (Chips) for 'Super' Ti-99/4A Homebrew Builders

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Joined: 14 Aug 2012 15:31

TMS99105 : Kit of ICs (Chips) for 'Super' Ti-99/4A Homebrew Builders

Post by lezanderson »

TMS99105 Super Ti-99/4A

For anyone designing or thinking of designing their own ‘Super’ Ti-99/4A microcomputer, I’ve asked a Chinese supplier to list a compilation of ICs which may help get you started. The Heart or Key to the list of ICs is the TMS99105, which is considerably faster than the original TMS9900 CPU.

As these Chips are NOS (New Old Stock) or working Pulls, they should be tested as these Integrated Circuits (ICs) are 35+ years old !

You'll find them here: ... SwsKddJfGv

Take a look at ;

For those not familiar with the CPU in the Ti-99/4A then take a look at : Wiki TMS9900

There’s also a most interesting project on YouTube :

Old ... c=236&st=1

Stuart Connors TMS9900 Stuff
Posts: 186
Joined: 14 Aug 2012 15:31

Re: TMS99105 : Kit of ICs (Chips) for 'Super' Ti-99/4A Homebrew Builders

Post by lezanderson »

Musings and ideas on the design of a Enhanced Ti-99/4A

Design Specification :

CPU (Central processor Unit):
TMS99105 24MHz processor. A improved and much faster version of the original TMS9900 CPU.

Memory System
Memory Mapper 74xx612 (74HCT612) to allow 1 Meg of RAM/ROM. The system would boot to 12MHz ROM/RAM system then copy ROM into fast SRAM (IS61C1024-xx, 128K SRAMs), then switch to a fast SRAM system running at 24MHz.

As in original Ti-99/4A with a TMS914 GPIB. With TMS9901,TMS9902 parallel / Serial ICs.

V9958 Video Chip with 192K DRAM (6pcs D41464-10s) and a CXA1645 TV Encoder.

A V9958 Video circuit/board design can be found here:
See ... design.htm

Sound & Joystick

SN76489, YM2149, SAA!099. By using multiple legacy 80s sound chips a sophisticated sound output could be generated.
The SN76489,YM2149 sound outputs could be mixed with the SAA1099 Stereo sound, to give left and right speaker stereo output. The YM2149 has parallel I/O ports, ideal for Joystick connection ?

Real Time Clock

Maths Coprocessor
AM9511 a legacy 70s maths coprocessor (or similar) would do fast floating point mathematics. The AM9511 is supposedly 8 times faster than the equivalent software routines !


AY-5-3600, intel 8279, legacy keyboard matrix readers giving ASCII type output.
PS/2 Microcontroller to read PS/2 keyboards
USB/PS/2 bought in board

Storage Devices:
SD Card PATA parallel type. Using a parallel I/O Chip as interface.
NVSRAM DS1250 type used as silicon disk
Floppy disk Drive , using a TMS99xx Floppy disk controller, though it is questionable that floppy disks are still relevant ?

Glue logic
GAL16V8,GAL22V10 for Glue logic instead of numerous slow TTL/CMOS chips.


There's an excellent series of Articles on designing a TMS9995 system in the Electronics today International (ETI). Though not strictly Ti-99/4A related it is still very interesting to read. ... _(Nov).pdf ... ran-Cortex
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