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Latching the MC output latch

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  • bill rowe
    Well poop, I ve been chasing a problem with the shield adapter circuit for days. I think I know what s going on though:I have an output shift register that
    Message 1 of 1 , Nov 11, 2013
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    Well poop, I've been chasing a problem with the shield adapter circuit for days.  

    I think I know what's going on though:
    I have an output shift register that gets loaded on OUT 6 from the MCs output latch. I can't load on the leading edge so i use a transparent latch and and by the trailing edge of the N lines the MC's latch is stable so that works.

    I need to maintain a stable parallel output independent of the shift register so I have a separate 74hc373 latch that is loaded on OUT 4.  Unfortunately, when N2 comes high, the 74373 goes transparent and its output is whatever was LAST written to the MC's latch because it still has not tripped because of a delay that accommodates the memory.

    I guess I need:
    -an edge triggered latch with an inversion of my current latch signal(maybe a 74374) or
    -a delay of about 4 us in my current circuit (not keen on this) or
    -a more sophisticated interface with the MC/1802's timing 

    So, looking at the circuit, I just replace the 373 with a 374 and REMOVE an inverter.  I can't imagine why i didn't do this to start with.  It also occurs to me that this is why i couldn't get it to work on a breadboard - there were just so many wires wobbling around i couldn't properly diagnose it.


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