Using Surgery to Teach an Old Dog New Tricks Steve Spiller

Backstory Friends since 6th grade … that’s over 30 years now Met through interest in the CoCo Sometimes annual summer vacation projects MAME cabinets Nintendo DS game ATARI 400/800/5200 game Using real hardware and tools

The TRS-80 Color Computer Originally released in 1980 by Tandy and sold at Radio Shack My first computer! 16k RAM Cassette deck cable Microsoft BASIC Motorola reference design MC6809E CPU <1Mhz MC6883 Synchronous Address Multiplexer (SAM) MC6847 Video Display Generator (VDG)

MC6847 Video Display Generator (VDG) Generates NTSC signal fed to MC1372 which forms a local transmitter for channel 3 or 4 Lots of “clones” simply built the block design from the VDG datasheet High resolution graphics was 2-bit but NTSC has magic: Artifacting! Bit patterns 0101 and 1010 produced color Which color was random

Genesis of a Project Looking for a project for the CoCo Hardware based FPGA in a cartridge Hardware tile engine ala Gameboy, NES VGA output Too ambitious F18A Project FPGA TMS9918A TI-99/4a, ColecoVision, MSX Full emulation CoCo VGA is Born Time to gather data

CoCoVGA Started out with full replacement Timing interactions with the M6883 were tricky and not documented Switched to a “piggyback” solution We plug in line with the VDG and snoop the signals

The Real Thing Approached by Ed Snider to move CoCoVGA into reality Refined our prototypes Designed PCB layout http://www.cocovga.com Other plans: Map registers into the address space Software control of custom hardware Wavetable/FM synthesis Try to take over the world

DONE!