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 From: M100 <[email protected]> On Behalf Of Fugu ME100 Sent: Friday, May 4, 2018 9:39 AM To: [email protected] Subject: Re: [M100] SPAM-LOW: Re: New member - question on 'half' alive Model 100 If the 80C85 is seeing 00H (NOP) it could quite easily run without generating an IO/M- line high. Although with NOP it should just keep going forever with incrementing addresses. If there was contention on the RD Cycle one or more of the data lines would look very bad, possibly sitting in between the threshold levels depending on who won the fight. 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: Friday, May 4, 2018 at 7:20 AM To: <[email protected] <mailto:[email protected]> > Subject: Re: [M100] SPAM-LOW: Re: New member - question on 'half' alive Model 100
