Re: [N8VEM-S100:5375] Z80 CPU board - D2/D3 port timing problem

[John Monahan <monah...@gmail.com>]

Traveling until Thursday Phillipe, so cannot help, possibly a 74xx14 instead of 74xx04,  may be of use somewhere in the circuit.
John

John Monahan (mon...@vitasoft.org)

On Oct 12, 2014 4:07 AM, "Philippe Elie" <philip...@gmail.com> wrote:

hi folks,

I finally identified the issued that made some CPM (non banked version) hang the system : the RAM bank switching system had a timing issue. More specifically, when the monitor initializes the D2/D3 ports (with 00 and 04 respectively) the second IO access was actually trigerring also a 04 write into the D2 port.

I solved the issue by replacing U25 74LS04 by a 74F04 but a little glitch on D2 port enable still appears that makes me a bit concern about the reliability :

I was wondering whether the problem would come from sOUT : for U39 I used a 74LS08 instead of a 74S08 thinking speeds would be the same and considering the CPU operates at 4Mhz  ? Do you that would fix the problem ?

thanks in advance for your feedback

Philippe

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