M-SoM A5 behavior to SD card chip select

Hello friends,

I'm trying to use one board developed to B-SoM with M-SoM.
But I have problems with the SD card
It uses pin 43 (A5) as chip select.
A5 has a different behavior in M-SoM, with 40K pull-down at boot, could this be the cause?
I also saw that the other pins used have differences in Internal pull resistance, But I don't think this can get in the way:
Pin 50 (MISO) / Pin 52 (MOSI) / Pin 54 (SCK)
B-SoM: 13K
M-SoM: 2.1K

Any possible configuration tips for using the A5 as a select chip for the SD Card?
And about the frequency at SD.begin()?

#include <Particle.h>
#include "SdFat.h"
SerialLogHandler logHandler;
int8_t SCS = A5; // chip select
SdFat SD;
SdFile file;
bool sdok;

void setup() {
sdok = SD.begin(SCS, SD_SCK_HZ(4 * MHZ));
 if (sdok)
        Log.info("sd card ok!");
        Log.info("sd card error!!");
void loop() { //// }

Hi, and welcome to the community!

What deviceOS version are you using? If you are using 5.8.0, please try 5.8.2.
There was a SPI bug present in the 5.8.0 version.

1 Like

I updated via the CLI and the problem was resolved, thank you very much. However, I was unable to update the firmware using the Web IDE as version 5.8.2 does not appear available for M-SoM devices.

Device OS 5.8.2 was added to the Web IDE yesterday. You may need to refresh to get it to display.

1 Like

Despite being implemented in version 5.8.0 (for M-SoM), in version 5.8.2 i can not choose which interface to connect to.

Error: Could not compile.
"no matching function for call to 'CloudClass::connect(spark::CellularClass&)"

Particle.connect() with a network type, such as Particle.connect(WiFi) was available in 5.6.0 to 5.8.1, but was removed from 5.8.2 and later because using it can lead to unpredictable behavior with automatic connection management.

It proved useful with M-SoM, but ok!
Thank you for the clarification