[SOLVED] NUCLEO-L432KC - can D7 and D8 be made to work?

All about STM Nucleo boards
Post Reply
Posts: 27
Joined: Wed Aug 21, 2019 1:59 pm
IDE: Arduino 1.8.9 & 1.8.3
Core: STM official, MightyCore

[SOLVED] NUCLEO-L432KC - can D7 and D8 be made to work?

Post by Andy2No » Thu Aug 22, 2019 4:43 pm

I had to ask, in the old forum, whether I could use pins D7 & D8, on the ST NUCLEO-L432KC Nucleo-32 (an Arduino Nano sized board, with not many pins).

Since that thread seems to be lost from the archived version, I thought it might be useful to summarise it here.

The card that was included in the packet showed all pins by name, including those two, so I assumed that meant they were connected. fpiSTM pointed out that the documentation does explain the default solder bridges. I'd read that, but it wasn't clear to me.

On a pinout diagram I found for it, which appears to be official, the D7 and D8 Arduino pins are shown as NC (not connected), but on the card in the packet, they're marked as PC14, for D7, and PC15, for D8.

It turns out the pinout diagram was right for that board - those MCU pins are used to connect a 32kHz watch crystal. They can be connected to the external pins, but only by some tricky looking (by my standards) SMD soldering.

If I'm reading the datasheet correctly, that applies to all the "L" (low power) Nucleo 32s, but not the "F" - so, if the number of useable pins is important, check before buying.

L432KC pinout as on card.gif
L432KC pinout as on card.gif (32.53 KiB) Viewed 890 times
(pinout as printed in the packaging)

Post by fpiSTM » Thu Jul 04, 2019 6:00 pm

Here, related documentations
https://www.st.com/resource/en/user_man ... 231744.pdf

You should read the user manual
https://www.st.com/en/evaluation-tools/ ... 432kc.html

Table 16. Arduino Nano connectors on NUCLEO-L432KC
D7/D8 shared with OSC32_IN/OSC32_OUT.

Then in §6.8 OSC clock

U2 pin 2 and pin 3 can be used as OSC clock input or as Arduino Nano D8 and D7 GPIO. There are four ways to configure the pins corresponding to different STM32 and clock usage (refer to Table 6).

You can also check in the schematics:
l432KC.png (12.22 KiB) Viewed 890 times

So if you want use them you have to modify the board (solder bridge).

In variant it is explicitly written:
https://github.com/stm32duino/Arduino_C ... .h#L37-L38

Code: Select all

#define PC14 7  // By default, SB6 open PF0/PC14 not connected to D7
#define PC15 8 // By default, SB8 open PF1/PC15 not connected to D8
Post by Andy2No » Thu Jul 04, 2019 6:42 pm


The part of the schematic you've posted has some text, just to the right of it, but none of that mentions the L432:

closed for L021, L031,L433
open for F042,F031,F303

I see you're right though - I held a bit of wire across those points, one at a time (fearing disaster), and that connected the LED for those brief moments when I managed to make a good connection.

I'll give some thought to whether I want to risk soldering on that scale, with my shaky hands... maybe not. They haven't left any room for making mistakes.

Post by fpiSTM » Thu Jul 04, 2019 7:04 pm
I know this is a bit confusing, in fact the pinout diagram is common to several Nucleo 32 form factor.
I always advise to read the user manual due to solder bridges configurations.
When I do the variant, I didn't see those pins were not connected by default. :roll:
Post by Andy2No » Thu Jul 04, 2019 7:06 pm
Noted. Thanks.

Also, I see these solder bridges are already closed, with a small rectangular SMD component:

Connect PF0/PC14 to X1
Connect PF1/PC15 to X1

- so I would have to desolder those too, and I probably shouldn't have been shorting either of the two bridges I want closed, with a bit of wire.

Thanks for pointing out the reason, anyway. I think I give up, and will just have to abandon the idea of using all the pins.

Post Reply