Hi,
I've recently bought my first oscilloscope, a Rigol MSO1074z-s so I am a very beginner in this field. I am making my first steps learning to use and discover its features. I've encountered with a strange behavior of the logic analyzer of the scope and I would like to ask for some advice or tips on it.
I was just wanted to try out the serial decoding so I've set up a microcontroller to send out the "Test" string over and over, with some delay, on a SPI port. I've connected the logic analyzer's test leads to the SPI lines and set up a decoder for those signals. For some reason on the MOSI line instead of correct bit signal form I had only some bursts and the serial decoder was unable to decode it. Firstly I thought that the problem is in my program but after verifying everything, I did not find any issue with my code. I tried to connect an analog test lead to the same MOSI line and there the bit pulses were appearing correctly and using this line as MOSI, the serial decoder was successfully decoding my data.
On the attached screenshot (LA_bursts.png) this issue is visible. On the upper part of the screen the bursts are visible on D0 input, labeled as MOSI. The CH1 lead is connected to the same point on my circuit, this is visible on the yellow waveform. I've set up two decoders. The upper one uses the D0 as MOSI input, the lower one uses the CH1 as MOSI.
Do you have any idea why this is happening? What I am doing wrong?
Thank you in advance!
PS1: At some point this started to work (LA_correct.png), but after turning the scope off and on after a short brake, the problem came back.
PS2: What I've tried:
- move the cables, clips, every connector to exclude loose connection.
- change the time base which automatically changes the sampling rate of decoder. On this scope I cannot change this directly. Any way, I think this problem is not coming from decoder.
- change the baud rate of the SPI from my code.
- change the trigger from MISO line to CS line.
- moved the MISO line to other input of logic analyzer. This actually solved the problem. This moves me toward the conclusion that my D0 line is not working all the time. It is strange because the other day I was able to do some decoding on RS232 using the same D0 line and worked perfectly for hours without a glitch.
By the way my firmware version is 00.04.03.SP2. I don't know yet if there is a newer version.