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

JohnBHanson · 15th Jan 2020, 8:54 am

Sounds like you are trying to run an 829 bios on an 849 system. The bits in the drive select register are different - but bios 3.4 should be able to cope with both I think.

Simple fix will be to jumper the GOTEK as drive C: which cpm should treat as drive B: if I have got my sums right. Then check with configuration as post 322.

Alternative is to modify the select routine - it can even automatically determine if it is a GM829 or GM849 by looking at bit 7 of port e5 (Should be zero for GM849 1 for GM829). Thats tricky with multi.mac as several bits of code need to be modified.

You might need a later bios for the floppy

I am not sure why write to the disk does not work - it could be that the floppy disk controller needs calibration but don't mess with that for the moment.

15th Jan 2020, 8:54 am	#326
JohnBHanson Heptode Join Date: Aug 2009 Location: Worthing, Sussex, UK. Posts: 661	Re: Gemini 80-Bus System Sounds like you are trying to run an 829 bios on an 849 system. The bits in the drive select register are different - but bios 3.4 should be able to cope with both I think. Simple fix will be to jumper the GOTEK as drive C: which cpm should treat as drive B: if I have got my sums right. Then check with configuration as post 322. Alternative is to modify the select routine - it can even automatically determine if it is a GM829 or GM849 by looking at bit 7 of port e5 (Should be zero for GM849 1 for GM829). Thats tricky with multi.mac as several bits of code need to be modified. You might need a later bios for the floppy I am not sure why write to the disk does not work - it could be that the floppy disk controller needs calibration but don't mess with that for the moment. Last edited by JohnBHanson; 15th Jan 2020 at 9:06 am.