SWD and JTAG

[achin]

Posted on February 17, 2016 at 16:44

I built my own board and I am trying to use the JTAG connections. It does not seem to work. It only uploads  a small percentage of time and even when it does, I am not to sure it is uploading correctly. I thought it was the reset circuit, because on the small amount of times I wanted to upload, I need to power cycle the board in order for the code to take action. I just tried SWD by random luck. It works really well. So, the question is, why does SWD work and not JTAG? With SWD, when code uploads, I do not have to power cycle the board. When I select JTAG in TrueStudio, are they expecting the 20 pin JTAG? I am kind of dumbfounded as to why one works well and the other does not.  Also, under JTAG, in order to upload code, I have to do a core reset. If I try a hardware reset, it does not work at all. 

[Tesla DeLorean]

Posted on February 17, 2016 at 18:09

The 20-pin header is just a connector, the active pins a subset of the total. Here we have JTAG and SWD functional with the 10-pin header configuration ARM has migrated too.

Perhaps you have issues with the pull-up/down configuration or wiring, it is really hard to surmise from the prose.

[achin]

Posted on February 17, 2016 at 19:23Do you have to add pull ups and pull downs? I just have a pull up for the reset line.  That being said, would SWD not require the pull ups/down and JTAG require them?

[achin]

Posted on February 17, 2016 at 21:38

Here is a dumb question. Is JTAG reset also supposed to go to the system reset pin?

[Tesla DeLorean]

Posted on February 17, 2016 at 22:00

NRST != NJTRST (PB4)

[achin]

Posted on February 17, 2016 at 22:32That explains a lot. What goes on PB4 then? Does the reset line on the connector go to the NRST pin?