The parallel cable III has reliability issues that you should fix when building your own.
- The parellel port has TTL outputs. It only guarentees a VOH of 2.4V. Using CMOS buffers with a switching threshold of 2.5V does not make much sense in that case. Instead use a buffer with a switching threshold between 0.8V and 2V. (For example CMOS buffers powered by 3.3V or skewed buffers.)
- The parallel port output can have a very slow rise time with a lot of noise. Connecting that to a fast buffer can create additional edges on the signals. You should have a significant hysteresis on the CCLK signal. You can do that by feeding the output of the CCLK buffer back to its input with a voltage divider.
The price is for the cable is good, but they will charge me $18us to send it in Quebec Canada. They used at it seems Global Express Mail and UPS ( it's a no go for UPS, they usually charge you $50 for every thing passing the border...).
Weather forecast for the week seem not good I'll maybe build a proto for the xilinx free cable .
Yes that what I'm gonna do. Thanks for your info :-)
We have produced a special version of our programming cable that has a narrow head called PROG2N. It is a Parallel III cable that has a 14 Pin IDC narrow end that fits most 14pin 2mm headers, the price of this is £10 and shipping is dependent on how quickly you want the cable.
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