VIA Plus: a small debug board for 128K/512K/Plus

[demik]

Hello everyone,

Posting this here, this is really niche. Built it while developing other stuff for early Macs

It's a small debug board that plug in place of the VIA (or on top of if you can find the correct clip). It includes a 7 segment display which is useful for displaying the following informations:

- /RESET status
- OVERLAY status
- RTC pulse (1 Hz)
- Vertical refresh pulse (slowed down to 3.75 Hz)
- Current sound volume level

Design is Open Source. Feel free to adapt it to others Macs or include it into something else like custom replica boards

oldworld/EDA/VIA Plus at master · demik/oldworld

Development ressources for Old World Macintosh (68k and NuBus PPC) and a few related things… - demik/oldworld

github.com

 

[mdeverhart]

That’s really cool, thanks for sharing!

 

[David Cook]

Fascinating. Clean build, too.

Tell us more about the values it monitors. What kind of issues can it help catch?

 

[demik]

That’s really cool, thanks for sharing!

Fascinating. Clean build, too.

Tell us more about the values it monitors. What kind of issues can it help catch?

Thank you. It's a passive devices. Two examples that happened
- tweaking ROMs or stuff plugged into the ROM slots. The display will display "o" because the overlay was kept active. Reason: damaged ROM socket: ROM not read, so overlay kept asserted
- black screen (CRT) display, no visible vsync on the (7 segment) display: dead LAG

Both issues could have been diagnosed with an oscilloscope, but somedays I'm too lazy to get the scope out
Note that I'm using this with a board where most components are socketed, this is my lab board that is used to test components

 

[David Cook]

The display will display "o" because the overlay was kept active.

Very clever.