Minimum connections needed between MCU and the st-link programmer?

[maryam magdy]

My MCU is stm32L432kc. I've concluded that we need a minimum of 4 connections: SWCLK, SWIO, vcc and gnd. Can someone from here confirm that?

And another question is I'm confused how to connect the Vdda/Vref+ pin 5 and the NRST pin4. Do I have to connect them? I have the schematic of nucleo board for my MCU attached. Should I just connect them the same way?

[Tesla DeLorean]

I'd lean toward having a pull-up on NRST, and also providing it on a debug interface, will help recover when the code does odd things, or sleeps the processor.

PB3/SWO/TDO is also recommended for a CM4 debug communication channel, ie SWV Serial Wire Viewer.

[Uwe Bonnes]

SWCLK and SWDIO and GND may also be enough. E.g. if VCC on your board is 3.3 Volt and you connect to the SWD connector on a nucleo or discovery board. NRST should have a 100 n to round. VDDA should at least be connected to VDD or clean voltage derived from VDD

[S.Ma]

GND, SWDIO, SWDCLK and MCU Vdd (for monitoring purpose) are the minimum required connectivity with ST Link for debugging.

[maryam magdy]

@Community member​  I'm guessing the SWO is the MCO in my nucleo board in the pic I attached. So without it I can't use the printf function and debug through serial?

[Tesla DeLorean]

No, I'm talking about PB3

The MCO (from PA8 on an ST-LINK) is presumably a clock source.