UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Gemini 80-Bus System

john_newcombe · 11th Jul 2019, 11:01 am

Having read a little more I can see that /NMI is triggered on a negative edge and that the signal is generated from the VSYNC of the CRTC which is what is holding it low and presumably not pin 15 of IC19 which is an input to the tri-state buffer.

So I am thinking that this is all a red herring and that I should investigate further why I see no IORQ despite the IN instructions within the code loop.

11th Jul 2019, 11:01 am	#157
john_newcombe Hexode Join Date: Apr 2019 Location: Skipton, North Yorkshire, UK. Posts: 252	Re: Gemini 80-Bus System Having read a little more I can see that /NMI is triggered on a negative edge and that the signal is generated from the VSYNC of the CRTC which is what is holding it low and presumably not pin 15 of IC19 which is an input to the tri-state buffer. So I am thinking that this is all a red herring and that I should investigate further why I see no IORQ despite the IN instructions within the code loop.