My system had previously been working fine with the Z80 CPU card and CP/M, but when adding an 8088 card the timing problem showed up.
A huge thanks to Dave and Thomas for this fix. John - perhaps it's worth adding to the IDE board write-up, as I suspect other will run into the same issue down the line. I did the modification on a small 14 pin header (I didn't want to modify the board until I was certain it would fix the problem). It worked nicely. - Gary On Tuesday, June 10, 2014 10:44:43 AM UTC-4, Thomas Owen wrote: > > First of all, I want to thank everyone for their generous time and > suggestions in resolving my Drive Selection problem. As John accurately > points out, there is a wide variety of old equipment out there and > sometimes you have to be prepared for the situations like this - mixing the > old and the new. > > That being said, however, is why I got the old IMSAI out of the closet > after many years - I really miss the tangle of cords, probes, extender > cards, and smell of smoke (that usually brings the wife into the room). > > I look forward to building more of the 'new' boards - I already have the > ZFDC and the Ram/Rom is on order. The CPU should be next but I with the > IMSAI and the Front panel, well, I hate to give that up so quickly. > So, I may have to deal with more of these little quirks that arise from > this chassis, front panel, and a 1977 CPU - and that is ok with me... > > Shown below is what my drive select now looks like - Originally I looped > the FF clock through unused gates just to get some delay, but then I took > Dave's (yoda) idea and simply inverted the signal from U15 pin1 through a > unused gate (U15 pins 4,5,6) and back to U16 pin 3. This places the RISING > edge square in the middle of my data on DO0 and the Flip flop changes as it > should. Is it perfect? Probably not, but it may work for others out there > fighting similar timing issues. > > Thanks again to all, > Thomas > > > Shown in the diagram is the Clock and Data inputs (pins 3 and 2) at the > Flip Flop: > > *Data bit 0 (Drive A):* > > > <https://lh3.googleusercontent.com/-g7iEwNvipXQ/U5cXmmYlSVI/AAAAAAAABYU/G_hfX5xoiuI/s1600/Data0.jpg> > > > > *Data bit 1 (Drive B):* > > > <https://lh6.googleusercontent.com/-8H5k1YdHZ2E/U5cYJZz1e1I/AAAAAAAABYg/EGOe8zjDASQ/s1600/Data1.jpg> > -- 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.
