Hi Phil,
A schmitt trigger has hysterisis, they make slow transitions and low level noise less of an issue. Remember a stepper driver is a potentially electrically noisy enviornment. Some people run long cables from PC parallel port. Long cables lead to slow transitions. A stepper is usally open loop, you can't afford missteps. I can't imagine not going to a cheap filter to guard against these issues.
Opto isolator typically would be slow enough not to respond. But they do present their own issues.
Yes on the extra inverters, use them or tie them off. I decided to use them.
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Phil, Still too many interests, too many projects, and not enough time!!!!!!!!
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