I would say your CPU looks good :) The ROM seems to be working as are all the buffers and ROM decoding, the code is executing correctly to the point of failure. The IO is still a possible source of error but as there are multiple accesses it looks like it performs the operations correctly.
Did you check the CE- on the RAM module? Just after that IN op RAM accesses start to happen. Without the NiCd the RAM might always start up with garbage which could cause some oddness. Interrupts are disabled so that should not cause problems. Looks like the RAM is the next target to investigate. From: M100 <[email protected]<mailto:[email protected]>> on behalf of Jeffrey Birt <[email protected]<mailto:[email protected]>> Reply-To: <[email protected]<mailto:[email protected]>> Date: Saturday, May 5, 2018 at 4:02 PM To: <[email protected]<mailto:[email protected]>> Subject: Re: [M100] SPAM-LOW: Re: New member - question on 'half' alive Model 100 Well, I know more…but I’m not sure what I know. I was able to capture the data bus (well the first 7 bits, used my 8th channel on the /RD* for the CLK input). I saved the output as a text file and taking account for the msb always being zero I was able to trace program execution to around here 7D4CH (DBH) IN E8H ; Scan Keyboard to test for CTRL-BREAK (cold boot indicator) where is goes wonky. I then put the LA on the IO/M line and was able to see it go high when reset held in and then go low, 5 short blips (for 5 in/out commands including the line above.) Then it is low for a short while and goes back high and stays there. By this point I’m bleary eyed from staring at the screen so much. One other bit of strangeness to note is that the modem relay was clicking on/off with the reset for a while and by the time I got a probe on M16-13 (Y2) it had quit. As I recall I did the same tests with and without the LCD/KB connected. I just noticed now that One gate of M20is shown down by the LCD connector in the schematic. It is buffering the output of a gate on M17 which is connected to the E pin of the LCD. I’m not sure what this is doing. Time for more research. I welcome any thoughts. Thanks, Jeff <snip>
