I have a continuous, 8-bit data stream of four characters "ABCD" running at 4Mbps. The pattern repeats and I want to verify that it repeats properly every time, so I would like to get a stable waveform on the scope when in normal trigger mode or use the decoder.
I've tried decoding this with SPI and setting the timeout to around each 8-bit segment (2 µs) and I cannot get it to decode. I have decoded a regular SPI stream that has some amount of delay between each 8-bit character, so I think missing this delay is confusing the scope.
I also tried decoding RS232 setting up the data rate, but I think needing a stop bit is throwing off the decoder.
I then tried triggering on one of the characters using both SPI trigger and RS232, and the scope will not see a character or pattern (i.e. LHLLLLLH for the letter A (65)).
I tried a couple other triggering schemes such as twiddling around a 4 µs holdoff; or setting up nth trigger on the clock, 127th edge after ~400+ idle time to get a trigger and it was not happening. I'm confused about nth trigger because I could not get it to run on the clock no matter how I set it up, I could just get one off trigger events when I twiddled the idle time or edge number.
I also tried recording 8 µs segments and scrolling through them in playback. I thought the scope might start a new recording every 8 µs, but it seems to use the displayed time scale for each segment (or frame).
I can of course single shot and zoom and scroll through the pattern, but keeping track of bits is hard, and the real test pattern is going to get more complex, so getting some sort of reliable trigger or decoding would help.
Here's some photos with the A character cued up to the start of the sweep. Each character takes two divisions.