ryaninspiron
Member
A bit of a mystery here, A while back I received an SBC200 that did not give any serial output. Shortly after, I was given a dual port ram EPROM emulator kit that a friend of mine designed, and when I load that with SDMON v3 (original monitor) and plug it into the first EPROM socket, the SBC loads into the monitor perfectly.
The problem is when I put in actual EPROMs M27C16 or EEPROMs AT28C16, Loaded with either of the two working monitors, (and with the SBC 200 configured with defaults jumpers for 2716) I get rolling nonsense characters across the screen every time. When I read back the data off of the EPROM it's completely correct.
And something is working right because even with the actual EPROM it's able to initialize the serial port (before spitting garbage) . And I get the exact same behavior when I try Glitch Works monitor program GW-MON 80 which also works perfectly on the dual port ram.
Serial output with Dual Port Ram
Serial output with EPROM of the same contents
Would love any ideas where to start with this, I certainly haven't seen anything like this before, and I was pretty sure that after the address selection stuff was out of the way it was a pretty straight connection between the Z80 and the EPROMS so not sure what this could be.
My near term goal is to boot off CPM with a Gotek floppy emulator (flash floppy) before going legit floppy once I have the ROM issues cleared up.
The problem is when I put in actual EPROMs M27C16 or EEPROMs AT28C16, Loaded with either of the two working monitors, (and with the SBC 200 configured with defaults jumpers for 2716) I get rolling nonsense characters across the screen every time. When I read back the data off of the EPROM it's completely correct.
And something is working right because even with the actual EPROM it's able to initialize the serial port (before spitting garbage) . And I get the exact same behavior when I try Glitch Works monitor program GW-MON 80 which also works perfectly on the dual port ram.
Serial output with Dual Port Ram
Serial output with EPROM of the same contents
Would love any ideas where to start with this, I certainly haven't seen anything like this before, and I was pretty sure that after the address selection stuff was out of the way it was a pretty straight connection between the Z80 and the EPROMS so not sure what this could be.
My near term goal is to boot off CPM with a Gotek floppy emulator (flash floppy) before going legit floppy once I have the ROM issues cleared up.
