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Mark1960 · 6th Jul 2021, 2:07 am

Problem was due to the wrong crystal fitted. I had a 7.3728MHz fitted instead of 4.4316MHz. The setup time for address to NADS falling edge is dependent on the clock. Tc/2 -150 ns. At the higher frequency its just on the edge of the data setup time for the 74LS395 to the falling edge on NADS. Capacitance from a finger or scope probe is enough of a delay for it to work.

If I’m going to try and overclock the processors I should probably change to a positive edge triggered register or a transparent latch.

6th Jul 2021, 2:07 am	#43
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,298	Re: Multiprocessing SCMPII on MK14 Problem was due to the wrong crystal fitted. I had a 7.3728MHz fitted instead of 4.4316MHz. The setup time for address to NADS falling edge is dependent on the clock. Tc/2 -150 ns. At the higher frequency its just on the edge of the data setup time for the 74LS395 to the falling edge on NADS. Capacitance from a finger or scope probe is enough of a delay for it to work. If I’m going to try and overclock the processors I should probably change to a positive edge triggered register or a transparent latch.