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
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.