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Old 3rd May 2018, 7:08 pm   #44
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Default Re: MK14 schematic revisions

Just managed to get first signs of life out of my MK14 replica,
now waiting for the 80L95, well 80C95 or 74LS365 and the RAM chips (ordered the AM9111 also).

I did have a fight with the new 74LS157 multiplexers (did not work as latch) and the fact that my temporary substitute RAM (HM6116) seemed to dislike the floating read, write and address lines of the CPU.

With 4 pullups on the top address lines and the read and write lines from the CPU the display suddenly got a lot more stable but still no 0000 00. I swapped the 74LS157 with an old set of 74LS257 (tri-state version of the LS157) and tada, steady display.

For testing the keyboard I used a DIL plug with a small PCB on it which carried a LS32 and a LS367 I had lying around and I could enter some data.
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