LoRa module not working with ESP32-C3's SPI interface

Community
#1

I have wired a LoRa module (SX1278) with the ESP32C3.

The LoRa module uses the SPI interface to communicate with the ESP32C3.

When I connect all the SPI pins to the C3, the sketch seems to stop executing.

If I remove the MISO wire and reboot, the sketch executes, but the LoRa module is not recognized.

I have checked the SPI pin assignments (MOSI, MISO, SCK, SS) and they are all okay.

If I connect the LoRa module to my ESP32-WROOM dev kit, it works perfectly.

Not sure what to do next to diagnose the problem.

Any help would be greatly appreciated.

Regards,
Anand.

#2

The problem is something to do with the way the ESP32C3 reads various pins at startup, with a bare bones SX127X in circuit the ESP32 goes into waiting for USB upload mode.

Fit pullup resistors to the LoRa devices NSS and SCK pins cures the problem for me.

#3

The problem seems to be that the SX1278 pulls down the MISO pin on startup. The MISO / D9 pin is used to put the ESP32C3 into BOOT mode, which is why the ESP32C3 gets stuck!
As @StuartsProject suggests, adding a pullup resistor on NSS solves the issue (NSS = high deactivates the SX1278 module).