TMS9900 Assembly Programming for the TI-99/4A
This is work in progress... This tutorial is planned to start in 2020

The TI-99 was pretty much the only computer to use the TMS9900, just like the Cpu itself, the TI-99 wasn't designed like most computers - with almost all it's ram as VRAM - it actually uses VRAM to store basic programs (which is not as fast as 'proper' memory!!)


TI-99 4A
Cpu 3mhz TMS9900
Ram 256 bytes! (32k ram upgrade option)
Vram 16k
Resolution 160x144
Max Tiles 256 (8x8 px) - 360 onscreen
Max Sprites 40 (8x8 px 10 per line)
Colors 4
Sound chip GBZ80 PAPU


TI Memory Map

Address  Details
>0000 Console / ROM / OS / GPL Interpreter / BASIC Interpreter
>2000 “Low” Ram Expansion (8k of 32k)
>4000 Device Service Routines
>7000 Cartridge ROM / Page Flip
>8000 RAM Memory Mapped Devices - VDP,GROM, SOUND, SPEECH.
>8000 CPU Memory 256 byte block
>8400 Sound Chip
>8800 VDP Data Read
>8802 VDP Status Read
>8C00 VDP DATA Write
>8C02 VDP Address Write
>9000 Speech Read
>9400 Speech Write
>9800 GROM Data Read
>9802 GROM Address Read
>9C00 GROM Data Write
>9C02 GROM Address Write
>A000 High Ram Expansion (24k of 32k)

TI VDP Memory Map

>0000 Screen Image
>0300 Sprite Attrib
>0380 Color Table
>0400 Sprite Descriptor
>0780 Sprite Motion
>0800 Pattern Generator
>1000 Free Space
>3500 Disk DSRs


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