A quick follow-up. I did some probing of the LS123 one-shots and I discovered something interesting. Pin 12 (Q-prime) on both U17 and U20 are free-running. The other one shots seem to be triggering properly. I don¹t see any immediate cause for this, so I swapped the chips but I get the same result.
Rich -- Rich Cini Collector of Classic Computers Build Master and lead engineer, Altair32 Emulator http://www.classiccmp.org/cini http://www.classiccmp.org/altair32 From: Richard A Cini <[email protected]> Date: Sunday, March 1, 2015 at 4:29 PM To: S100-Post <[email protected]> Subject: MiniFP build - data bus question Guys ‹ I finished my MiniFP board this morning and I can¹t seem to deposit to or read from memory using the EXAMINE toggle. The ³next² part of the function works, so I can step among addresses but the data LEDs are all on all the time (unless I set JP5 SSW_DSBL jumper). However, if I use the SINGLE_STEP switch, the data bus LEDs appear to reflect memory contents. The experimental system is very simple CompuPro RAM17 (64k), IMSAI 8080 board, and the front panel. Before I say that anything is wrong, can someone confirm the jumpers? I think only the MWRT should be jumpered. The RAM17 is an IEEE-696 board so as I do for my IMSAI, I¹ve isolated pins 20/70 (UNPROT/PROT) on that board. Chip-wise, I¹ve used LS (including the LS123 as recommended in the Wiki) except the 7402. I don¹t have any 7400¹s in-stock so I¹m using LS00 for nowŠdon¹t know if that¹s part of the issue since those gates are used in the EXAMINE circuit. I replaced the 8212 just in case, but that had no effect. The data cable is fine. Any help, even questions to get me thinking, would be appreciated. I feel I¹m pretty close to a solution here. Thanks! Rich -- Rich Cini Collector of Classic Computers Build Master and lead engineer, Altair32 Emulator http://www.classiccmp.org/cini http://www.classiccmp.org/altair32 -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
