[milesvp]

Word of warning. I lost several days of debugging what looked like a working serial bus using a logic analyzer. I was about to give up when a friend asked what it looked like under the scope. The problem jumped right out at me. Certain bit patterns would distort the signal and I wasn’t crossing a threshold. Solution was trivial to fix after that, just replace a pair of pull up resistors and the scope showed good squares again. Had a similar problem with an optocoupler after that. Logic analyzer hid the fact that the optocoupler was too slow, and none of the leading edges were ever square. Ended up replacing that outdated part with a similar priced newer part. My client at the time was strggling with a whole batch of these optos for a number of SKUs that were within spec, but the variance was so high that it was common to get a batch that weren’t good enough for his designs.

[HeyLaughingBoy]

Haha. I remember having exactly the opposite experience about a year ago. I was debugging serial communications with a scope and everything looked perfect. Couldn't understand why it worked at power up and stopped working a few seconds later.

However, looking at the data on a logic analyzer and being able to see several seconds of data at once showed that the external module I was trying to interface with was buggy. Turned out that the unit we had was a preproduction prototype!