Debugging USART using Saleae logic probe

[LinkMTech]

Embarrassed? I think it's exciting to find new tools and uses!
How do you like your Saleae? I think it's money very well invested and has saved me so much time and headaches especially when it came to watching DT's interrupts at work.

[Demon]

I love it. I'd prefer the 16, but the basic 8 channel model is more than enough for the hobbyist.

I have 2 oscilloscopes. I don't use them enough to remember how to calculate the time bases to get hertzes. I take them out whenever I want to test switches and debouncing though.

I'd love a USB scope, but money is real tight so that's out of the question until I win the lottery.

Robert

[LinkMTech]

I thought about the 16 also but couldn't imagine what I would test with all those yet!
I barely hit 6 while playing around with an accelerometer + gyro, DT's INT's, test points, etc..

[Demon]

I've been doing my testing and research in the kitchen using my laptop this winter; it keeps me closer to the family.

Problem is my laptop has the wrong sex serial connector so I can't use the same cables I've been using on the desktop PC downstairs. Of course I always forget to buy an adapter and was forced to use an LCD to debug.

And this is where things got tangled with this project; all my pins are busy except RX1/TX1 which will be used for comms. No problem, I pulled out another breadboard that has an LCD and will display there. Wrong, can't figure out why data isn't sent properly.

The Saleae confirmed that the message leaves the master just fine so it's 50% solved (picture above). The data is lost as soon as I connect the slave PIC. The sad part is that I had all my breadboards talking together just fine last summer but I'm apparently too dense to figure this one out. Yes, I was using these same PIC models too, argh....

Robert

[Demon]

I spent all afternoon and then some yesterday trying to get these talking.

Had them working in 5 minutes after posting. LOL

I gave up and did the equivalent of stopping and asking for directions; I looked at my code from last summer real close and noticed this comment:

'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
'                   RX must be input or else USART disrupted                   x
'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I can't remember where I got this (didn't notice in the manual if it was there), but that was the problem.

Robert


EDIT: Now I remember, it was from the datasheet:

For all modes of EUSART operation, the TRIS control
bits corresponding to the RXx/DTx and TXx/CKx pins
should be set to ‘1’. The EUSART control will
automatically reconfigure the pin from input to output, as
needed.

[ozarkshermit]

Not related totally, but I absolutely LOVE my Saleae Logic.

I just used it again today to determine some Infra Red codes from a remote transmitter. I don't use it all that often, but it has helped solve some otherwise very troublesome problems.

Ken

[Demon]

Neat. Can you provide details how you did it?

It's one of those things on my To Do Whenever list.

Robert