Hello everyone,
Yesterday I found my miniLA device which I built about 6 years. I have original PCBs the same as these presented on project webpage. I also found an USB interface original PCB and couldn't resist to mount and test it.
I have a following problem, my miniLA works fine when connected to my older computer via LPT port. No communication problems, even with a 5m long cable.
But it doesn't work with USB interface. I started to get very deeply into the whole thing, even looked into the source code, learned the EEP protocol basics, looked at the waveforms on the oscilloscope. This problem made me mad :).
In my USB interface I used FT2232D which is backward compatible with FT2232C. I also used 74HCF4053 multiplexer because I didn't have 74HCT but there are no very many differences between timings of these devices.
It looks like the USB interface works on the edge. Sometimes, every few seconds application gets a proper reading of firmware version from the device. But /DST and /AST signals are delayed compared to /RD, /WR, ALE signals because of this multiplexer which is not fast enough for 6MHz signals. I seems that as the result, device and PC doesn't latch the proper value of data bits.
The second problem is that address write signal changes to low exactly the same time as /AST strobe. Shouldn't it be settled at least a clock cycle before /AST?
I'm going to order some different versions of 4053 multiplexer and then compare the results, maybe a little faster IC will make it work without problems. I'm not sure if there are any important timing differences between HC. HCT, HCF, HEF versions of these devices.
Or maybe a problem is somewhere else. Did anyone have similiar problems with USB interface?
Mateusz SQ3PLX