Re: [N8VEM-S100:4063] Re: CF IDE card checkout and final assembly problem

Never mind DO0 comes directly off the bus.

Dave

On Monday, June 9, 2014 12:18:25 PM UTC-5, yoda wrote:

Well if U7 is not active (which I think you are right - going thru the truth table of the logic feeding it now) how do you expect DO0 to change? The is where the signal is coming from. That may be the crux of the problem?

Dave

On Monday, June 9, 2014 12:01:25 PM UTC-5, David Fry wrote:
Dave,

have a quick look at gates U6C, U6D & U11F

U7 will not be active for port address 034H

Thomas,

out of interest what CPU card are you using ?

regards

David Fry

On Monday, June 9, 2014 5:45:01 PM UTC+1, yoda wrote:

John

I will say it again - the type of CF card can have no effect on this circuit. Why is DO0 run through the 7407 anyways - it is already buffered at the 244 U7? I think there is so much delay introduced in the circuit that DO0 is never really stable when it is clocked into the 7474. I think it is a race situation and you are lucky if it can ever be deterministic. I guess one thing that might be tried is to eliminate the 7407 by bending out pin 2 of U16 and connecting it to pin 18 of U7? Don't know if that is going to help or not. Thomas can you put logic analyzer on pin 2 and 3 of U16 so we can see the timing relation between the 2 signals - that will tell what is being clocked in.

Dave

On Monday, June 9, 2014 11:19:35 AM UTC-5, monahanz wrote:

Sorry I meant actual CF card itself, Kingston, etc..

John

From: n8ve...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Thomas Owen
Sent: Monday, June 9, 2014 9:16 AM
To: n8ve...@googlegroups.com
Subject: [N8VEM-S100:4063] Re: CF IDE card checkout and final assembly problem

John,

It is the newest batch I believe, '02a'.

Thanks

On Sunday, June 8, 2014 7:58:45 PM UTC-4, Thomas Owen wrote:

All,
I had posted this to the thread dealing with ordering this card, but decided to post a new topic dealing with the problem I have had with final checkout of the board.

During assembly the board passed all the 'in progress' checks. The final steps were to output to different ports:

I have output the following and everything passes:

QO33,80 ; Configures ports A, B and C as output ports
QO32,2B ; Selects right hand pair of digits
QO30,01; display 01on right digit pair and work through each bit - all ok

QO32,2c; Selects middle pair of digits
QO30,01; Should display 01 on middle digit pair, work through each bit - all ok

QO32,2d; Selects left hand pair of digits
QO31,01; Should display 01 on left digit pair, work through each bit - all ok

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.

Thanks,
Thomas

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