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

JohnBHanson · 16th May 2019, 5:33 pm

Just another thought - are you running RP/M via the serial port. If so remember CP/M is configured to run on a video card.

To change that look at track 0 sector 31h (Using 128 byte sectors). This sector starts with
C3 xx xx (17 times) and is the bios jump table. at offset 33h in this sector is a byte (15h). Change
this to 14h will make CP/M use the serial port.

You might find that is why you are not seeing anything on your screen and actually CP/M is booting to the video card you cannot see.

All numbers are in hex and are the result of using he disked program (Type ? to get help)

16th May 2019, 5:33 pm	#53
JohnBHanson Heptode Join Date: Aug 2009 Location: Worthing, Sussex, UK. Posts: 661	Re: Gemini 80-Bus System Just another thought - are you running RP/M via the serial port. If so remember CP/M is configured to run on a video card. To change that look at track 0 sector 31h (Using 128 byte sectors). This sector starts with C3 xx xx (17 times) and is the bios jump table. at offset 33h in this sector is a byte (15h). Change this to 14h will make CP/M use the serial port. You might find that is why you are not seeing anything on your screen and actually CP/M is booting to the video card you cannot see. All numbers are in hex and are the result of using he disked program (Type ? to get help) Last edited by JohnBHanson; 16th May 2019 at 5:35 pm. Reason: Make sure reader understands numbers are in hex