SparkFun Forums

[Daniel Wee]

I have some questions concerning the programming interface for the STM32 MCU. Putting aside the serial bootloader - am I correct to say that the absolute minimum programming (not debugging) requirement would be:-

SWDIO
SWCLK
GND
VDD

with NRST as an option. Is this a correct assumption? All the documentation I could find regarding this mention this as a debugging option and do not explicitly mention that this is sufficient for programming.

Further to this, I would just make an adapter to connect the J-Link's 20-pin JTAG header to connect these pins to program it in this reduced mode? Is there a schematic of the adapter, assuming that some other connections need to be made such as grounding some of the JTAG pins and so on?

My objective here is to have a minimum pin-count interface (excluding a serial bootloader) and using a J-Link JTAG to do the job (thus requiring an adapter.)

Any help in this is much appreciated.

Daniel

[TheDirty]

Speaking only with experience with the LPC1xxxx SWD programming, reset is not an option. 3.3V is sometimes an option depending on your programmer, but generally you need 5 pins. 3.3V, GND, SWDIO, SWCLK, and RESET.

Search SWD connector for the standard 10 pin 1.27mm SWD connector. I've tried using a 5 pin inline connector and for some reason it's not working for me, but if I green wire in the 10pin connector it works. I haven't figured out why, yet.

[Daniel Wee]

Thanks! At least I know I'm somewhat on the right track. I'll try to figure out if 5-pins is enough.

Daniel

[TheDirty]

Well, I only use 5 wires, but with the 10pin connector it always works for me, but they are pretty expensive. A 5 pin 0.1" header takes about the same space, but is cheaper. I only tried the 5 pin connector on one board, but I could not get it working for some reason. It must be something I'm doing, but I checked over the wiring over and over and couldn't figure it out. If I just soldered wires onto the same board directly to a 10pin connector it worked fine.

Again, this is with the LPC1xxx's.

[rmteo1]

You need just 4 connections to program and/or debug.

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