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Old 26th May 2020, 9:06 pm   #258
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
Default Re: Recreating the Bywood Scrumpi

OK Good news the alternate AMD9112 chips turned up - same day as the long delayed DM2112 ones... and both sets work fine in the board. Except as soon as I turned off PROTECT to allow some self modify code it wiped RAM. Turned out I was correct and one of the gates on my 74LS00 was faulty as shown by my chip tester. Managed to find one working one in my MK14 VDU kit and now the board works as I expect with some flashy code running to HALT, SINGLE STEP, SLOW - data entry is a breeze now you don't have to pull a jumper wire every time you want to write.

The only problem I seem to have is I still cannot get the latch to work - putting it on the dual scope it is now getting the missing clock pulses I was searching for before since I put in the new 74LS00... should have trusted my kit... it seems that the clock pulse is not arriving while the CS is LOW although it is a little hard to see exactly on a 1979 HAMEG with the Dual Channel being a bit choppy... very retro and authentic diagnostic experience.
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