Hi, I can vouch for the ATOM mask ROMs occasionally failing. I have a dead one here as well. ![:cry:]( "Crying or Very sad")
If the files you propose to are both exactly 4096 bytes then I don't see why that should not work. I _think_ it should be BASIC first. The way the ATOM addresses the mask ROM is a little odd tho -- the 2 halves appear at different places in the memory map -- so don't just take my word for it unless you have an EPROM eraser!
The MS signal comes from IC8.3, part of the address decode logic. It is an input to the 3 buffer ICs27/8/9 as well as IC31. With that signal stuck high the 6847 has permanent control of the video RAM, and the MCU can not write to it: the buffers aren't enabled. It _might_ be that IC08 has failed.
IC8.11 is also used to decode the addresses for page zero RAM (ICs51/2). If IC8 totally fails the machine will not work well at all.
Good luck. I will be watching your progress!
Pete
If the files you propose to
Code:
catThe MS signal comes from IC8.3, part of the address decode logic. It is an input to the 3 buffer ICs27/8/9 as well as IC31. With that signal stuck high the 6847 has permanent control of the video RAM, and the MCU can not write to it: the buffers aren't enabled. It _might_ be that IC08 has failed.
IC8.11 is also used to decode the addresses for page zero RAM (ICs51/2). If IC8 totally fails the machine will not work well at all.
Good luck. I will be watching your progress!
Pete
Statistics: Posted by MrSquiggles — Sat Apr 19, 2025 8:04 pm