MC6847 test circuit (part 8)

When you see the image above, what do you think of? It is a video capture of a real TRS Color Computer (CoCo) screen.Nah, it is just a CoCo emulator, and the host HDMI output was converted to composite video just to look old. If you answered 2 you are not entirely right, and if …

MC6847 test circuit (part 7)

This is going to be a short article. The other day I was researching Composite Video mods for the TRS-Color computer (which uses the MC6847 as video generator) and found a video describing a S-Video mod instead. The advantage of S-Video over Composite Video is that luminance (how bright the image is) is carried separated …

MC6847 test circuit (part 6)

AS we have seen in a previous article, the MC6847 Video Display Generator was designed to be used with the MC1372 Color TV Video Modulator. It is this second chip that actually generates the composite video signal ready to be used by a TV set. MC6847 connected to MC1372 Four pins on the MC6847 connect …

MC6847 test circuit (part 5)

Composite video image captured from a MC6847 The tests we have done so far use only static data for drawing the screen. Data is presented to the MC6847 either by hard-wiring data bus to address bus, or by wiring the data bus and address bus to an EEPROM. This time we will use a CPU …

Troubleshooting a Disk II controller card (part 2)

With the Disk II controller card in (hopefully) working condition, it was time to move on to the main part of this project: build an emulated disk drive using a Raspberry Pi Pico. I had a rough idea on how to do it: The Disk II is a 5V device, while the Pico is 3.3V, …