Thread: Ortonview PCB
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Old 14th Sep 2021, 8:04 pm   #497
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: Ortonview PCB

I don’t have capacitors fitted, but I did have a scope probe on A10. I’ll try again with the scope probes removed.

Also need to fit the 8154 and key in Slothie’s test code, and maybe also try with the extra extra 1.5k ram.

Operation of the circuit is as follows, hopefully this doesn’t cause more confusion.

NADS low presets the first flip flop, which holds clear low on the second flip flop, holding 8060 NENIN low.

NADS stays low until after the XOUT rising edge keeping the first flip flop set.

After NADS returns high, the first flip flop remains set, keeping clear low on the second flip flop and 8060 NENIN remains low.

On the next XOUT rising edge the first flip flop is cleared, this releases clear on the second flip flop, but too late for XOUT to clock in NENIN from the PIC, so again NENIN to the 8060 remains low.

Then on the next rising edge of XOUT, NENIN from the PIC can be clocked through to the 8060.

The extra connection from /Q of the second flip flop to clear of the first flip flop ensures that after NENIN to the 8060 has been raised, NADS can not set the first flip flop. This relies on the “feature” of the 74x74 where both clear and preset low will hold both the Q and /Q outputs high.
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