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Re: [N8VEM-S100:6351] Re: 80386 CPU Board - A possible solution

John -

Will give this a try over the weekend.

The V3 sounds fantastic, perhaps using switches that are widely available thru Mouser or Digikey would be helpful. 

- Gary

On 2/19/2015 1:51 PM, John Monahan wrote:

Gary, took another look at this V2 SMB,  U33, the 74LS175 is clock triggered on the rising edge. The signal coming from U31B (pin 6) may be arriving too late and somehow the data bus has lost it by the time it rises into U33.   I’m seriously considering doing a V3 SMB using a few GAL’s and more functionality, since I don’t have your problem could you check if this is the problem.


We will invert the signal coming from U31 pin 6, so the start of the rising pulse will latch the data lines into U33.  Fortunately the is a spare gate on the board U10B,  a 74LS00.  Jumper its pin 4 to Vcc. Bend out pin 6 of U31B. Jumper this pin to pin 5 of U10. Jumper U10 pin 6 to pin 9 of U33.   Then see if you can get home with the 80386.