Sorry I meant actual CF card itself, Kingston, etc..
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Thomas Owen
During assembly the board passed all the 'in progress' checks. The final steps were to output to different ports:
QO33,80 ; Configures ports A, B and C as output ports
QO32,2c; Selects middle pair of digits
QO32,2d; Selects left hand pair of digits
All displays are correct.
Now the final step is the Drive Select and that is where I am having trouble:
Board always comes up with 'Drive A' selected
Now, QO34,0; no change
Reset, start again:
QO34,1; no change
I can never select drive B.
Several generous members (thank you David Fry) have made suggestions, and here is where I now stand:
My preliminary check this afternoon shows me that there is a timing issue at U15, the 74ls02. Using my logic analyzer and monitoring the inputs and the output (which clocks the drive select flip flop) I see a big timing difference between SEL_SECOND and WR.
What this means is that the output of the gate never goes high allowing the bit change to effect drive change/selection.
I am going to get some screen shots from the analyzer tomorrow, and if anyone has any suggestions I would greatly appreciate it.