While working on his CoolRunner-II 50Mhz counter project jbaele found a bug. The reset line was showing a serious glitch when the stop signal was sent to the counter. The glitch was found to be the result of having the stop and reset signals next to each other on a ribbon cable. The capacitance of 14pF between the wires had enough leakage to hamper the project.
Via the forum.
Get the CoolRunner-II development board for $15 and XC9572XL dev-board for $15.
Leakage? I would say crosscoupling at overshoot on non-terminated transmission line.
With a bench setup like that, it’s a wonder anything works.
@Drone: ok, fair enough… but with older logic chips, eg 74HC/HCT and slower, you can often get away with this kind of prototyping. I just wanted to note with a CPLD like CoolRunner-II that can generate sub-ns edges (for low output loads) you have to be more careful about signal integrity. Per datasheet, as the load capacitance goes to zero, the output risetime approaches 0.3 ns which is pretty fast!