STM32F429B JTAG Works, SWD not!

[Vahid Ajallooeian]

Hello dear engineers,

I have made a custom header board based on the STM32f429BIT6. The board can be programmed with the JTAG interface. AS SWD and JTAG share the same connection, (JTAG needs more connection), I assumed that it would be possible to change the programming type from JTAG to SWD in software. but it doesn't work. the pull-up and pull-down resistors are established and have not been forgotten. Is there anything I might have neglected so that I wasn't able to use SWD Interface? I use Jlink V8.

Your help would be appreciated.

[Petr DAVID]

Hello Vahid Ajalluian,

According to reference manual RM0090 the external resistors should not even be necessary. By default, the JTAG-Debug Port is active. If the debugger host wants to switch to the SW-DP, it must provide a dedicated JTAG sequence on TMS/TCK (respectively mapped to SWDIO and SWCLK) which disables the JTAG-DP and enables the SW-DP. More about this sequence could be also found in the mentioned reference manual more specifically chapter 38.3.1 on page 1685.

I do not know much about segger Jlink V8, but I would definitely try to check all the connections and I would maybe recommend you to try contact segger directly.

[Vahid Ajallooeian]

Dear @Petr DAVID​ 

So far I saw that while the chip can be programmed via UART, it is not able to be programmed with the JTAG port while external resistors are not soldered. No matter it is J-link or ST-link

[Tesla DeLorean]

Post salient portion of schematics. Used F2/F4 with JTAG and SWD interchangeably here

Doing something strange

[Vahid Ajallooeian]

Dear @Community member​ 

Sorry for the late reply.

Attached is the schematic and PCB of the board. Nothing special is in, since the board is about to be a core board. What I meant about soldering pull-up and pull-down resistors was about to solder them on air! :grinning_face_with_sweat:

[Tesla DeLorean]

Can you attach as a PDF, thanks.

[Vahid Ajallooeian]

Dear @Community member​ 

Here is the pdf

[Tesla DeLorean]

Looks reasonable enough, non-standard header, doesn't match ARM's or MIKROE's

Make sure NJRST isn't used or mixed with NRST on SWD use case.

Here I've used the ARM 10-pin Cortex Debug Header, and that connects via SWD or JTAG