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T > TEXAS INSTRUMENTS  > TI 99 / 4A     

Texas Instruments
TI 99 / 4A

The Texas Instrument TI 99/4A was a very succesful computer. A large number ROM cartridges (36 KB each) were developped for this computer, as the popular Extended Basic.

Up to seven peripherals could be connected : 32 KB RAM extension, RS232c, Disk controler (90 KB per disk, up to 3 disk-drives), speech synthetiser, Peripheral Expansion box, and so on... One item of note is that the bus architecture for the Peripheral Expansion box (PE) was the basis for the NuBus used in the later Macintosh computers.


Contributors : Stephen Boutillette

Ben Yates says :
The TI VDP had 16K of dedicated VRAM, outside of the CPU RAM memory map.
The 99/4A has 4 VDP modes :
1. Graphic I (32x24, 255 redefineable characters, 16 colors, 1 background and 1 foreground color for each character set of 8 characters, 8x8 character matrix)
2. Text mode (40x24, foreground/background colors out of 16)
3. Multicolor (weird 48 x 64 mode, 4x4 unicolor character matrix)
4. Bitmap - same as 1, except 768 characters and each character can have a foreground and background color (of 16) for each pixel row of that character.

David Stites adds:
You list the TI 99/4a as being released in June 1979. At about that time I purchased a TI 99/4 for around $700. Besides the built-in BASIC and the firmware cartridges it had a third function called an Equation Calculator. I never used it and when the computer went insane they replaced it with the /4a for $50. The /4a didn't have the Equation Calculator.



There''''s an interesting site about TMS99xx stuff :

Has quite a lot of stuff on the TI TMS9900/TMS9995 hardware including a breadboard self-build computer based on the TMS9995

Well worth a look !

Friday 18th July 2014
Mark (USA)

Like Jim O., I enjoyed countless hours programming (mainly for the speech synthesizer) and playing what few games my friends and I shared.

What hasn''t been mentioned here is that, due to the motherboard''s unusual design, you could not place these machines on a metallic surface during operation. This would cause components to misbehave and overheat due to induction currents in a few of the coils.

Still, despite its crippled design, it was a fun computer to use.

Sunday 9th February 2014
Kelly Roach (United States)

Monday 30th July 2012
frank (us)


NAME  TI 99 / 4A
MANUFACTURER  Texas Instruments
TYPE  Home Computer
YEAR  1981
KEYBOARD  QWERTY full-stroke keyboard, 48 keys
CPU  TI TMS 9900 (with 256 bytes 'cache', actually it accesses to 256 bytes of RAM)
SPEED  3,3 MHz
CO-PROCESSOR  TMS 9918 (TMS 9929 in Europe) - Video / Sprite
RAM  16 KB - Memory expansion card can be added : 4 KB or 32 KB (up to 52 KB)
ROM  26 KB  : 8 KB ROM connected to the CPU + 18 KB ROM in byte-serial bit-mapped circuits (usually known as GROM, Graphic Only Memory)
TEXT MODES  32 x 24 (16 colors), 40 x 24 (2 colors)
GRAPHIC MODES  Multicolor mode : 48 x 64 with 16 colors
256 x 192 with 16 colors (only accesed via machine code)
Sprites (only with TI-Extended Basic)
COLOrsc  16
SOUND  3 channels, 5 octaves (110hz to 55khz) and 1 noise channel (periodic and white)
SIZE / WEIGHT  38 x 25,5 x 6 cm / 2,15 kg
I/O PORTS  Tape interface, RGB video, Joystick (2), cartridge slot (Solid State Cartridge)
OS  TI's own system, but a p-code card could be added, which gave access to the UCSD p-system and a Pascal compiler.
POWER SUPPLY  Special TI external PSU
(pins 1,2 : 16v / 1,6A -- pins 2,4 : 8v / 0,15A)
PRICE  £99 (UK, 1983)



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