View Full Version : Vector Graphic Z-80 Rev 1

January 7th, 2016, 06:01 PM
Anyone have the manual for the VG Z-80 Rev 1 CPU board? I can only locate the Version 2-A PDFs in the usual places.

January 8th, 2016, 07:57 AM
I confirm that I also looked everywhere and only rev 2A is available.

January 8th, 2016, 08:46 AM
The one obvious change between Rev 1 and Rev 2 is the addition of U18 in the latter, a 74LS02 between the Z80 pin 21 bar-RD line and U4.

I've been trying to get this card to work with the IMSAI CP-A. Something is going on with RUN stuck high. Not sure why the 8T97 on the CP-A can’t pull it low. It seems like it can't sink the current from the +5V pull-up on the Z-80 CPU. Probably entirely unrelated to the missing U18.

EDIT: That was a silly idea. Based on the CP-A docs, I hunted the problem with my machine stuck in RUN down to the XRDY line. The 7430 at U21 was borked, with no output registering on pin 8. It's stuck SORT of high, but probably due to the pull up on the Z-80 board. Switching with the 74LS30 at U9 brought some functionality back to the front panel: stop / run / examine / deposit. Progress!