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Old 10th Jul 2019, 9:08 am   #149
NealCrook
Tetrode
 
Join Date: May 2019
Location: Reading, Berkshire, UK.
Posts: 51
Default Re: Gemini 80-Bus System

Well, it's good that you can blip reset successfully from the host.

Your comments about getting the IVC message even when the board is not selected suggest that the local cpu should initialize the display even without any encouragement from the host, so that suggests there is little benefit (yet) in worrying about that blob of circuitry in the top left corner of sheet 1.

I am puzzled why the dot clock is not being selected reliably by the tiny test program.

I suggest going back to my original select everything in turn rom and taking a look at the crtc CS and E signals per my earlier post

If they look ok then I suggest going back to the proper to. And having a probe around..

- is the crystal dot clock selected
- are any outputs from the crtc toggling.. particularly the address and row select lines going to the chargen and display rams
- if yes to both the above then guess that the cpu has set everything up ok. So look at the final shift register load/clock pulses as I mentioned before and follow the video data and hsync vsync logic through to the output.

- you can also check that the other outputs of the latch look correct.. like the display enable and reverse video.

Neal
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