FYI - I am using the 68K running at 6MHz so it is not specific to Z80 - Sorry for the mistake above - I had not traced the truth table all the way thru - so U7 is not active - I forgot the DO0 comes directly from the buss - with the logic analyzer experiment above we should be able to see what is going on. The solution may be another issue - I should have some traces tonight when I get home from work.
Dave On Monday, June 9, 2014 12:25:18 PM UTC-5, monahanz wrote: > > This is a real old board, in fact I think it was the first board I laid > out (back in 2009), no excuse I know, but I would do it slightly > differently now. > > > > For sure mine works fine. I can pip A: to F: with verify with CPM3 no > problem with the 10MH Z80 board. Works with the prototype 80386 fine as > well (which is way less forgiving in terms of timing). Never a problem with > the 8088, 8086 or 80286 boards. In fact that IDE board is one I can really > count on. So I’m at a loss to understand the problem. I using two boards > labeled Version 02. Hopefully it’s not something about V02a > > > > The reason DO0 has its own input and not taken from U7 (the boards > bidirectional data bus) Dave is that I wanted to make sure the data line > would never be “glitched” . The 8255 is always connected to that > bidirectional data bus. When you change modes with the 8255 strange > (transient) things happen with the data lines. This was mentioned in one > of the earlier articles mentioned that I based the design on. > > > > If there is a race condition, Thomas can you drop the Z80 down to say 2MHz > and see if the problem persists. If a problem we can try delaying U15A’s > pin 1 to the FF with a resistor/cap, or using a 74L02. > > > > The above said we need to get to the bottom of this because it’s a must > that this board is reliable to go forward building these S100 systems. > > > > John > > > > > > *From:* [email protected] <javascript:> [mailto: > [email protected] <javascript:>] *On Behalf Of *Thomas Owen > *Sent:* Monday, June 9, 2014 9:16 AM > *To:* [email protected] <javascript:> > *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 > > -- > You received this message because you are subscribed to the Google Groups > "N8VEM-S100" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] <javascript:>. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
