If you don’t have a 32 bits arduino board using a serial pass-through sketch you can follow this method. Instead of using separate wires to all the necessary pins of the shield, you can plug the shield into an Arduino and connect the RX, TX and the GND of the USB-to-Serial converter to the top of the shield (RX=D0, TX=D1).
The sketch on the Arduino should do the following:
pinMode(7, OUTPUT); digitalWrite(7, HIGH); pinMode(0, INPUT); pinMode(1, INPUT);
I’m setting pin 0 and 1 (serial connected to SARA-N2xx) to input, so that we’re sure it will not conflict with the serial converter. This way you should be able to start the firmware uploading process.
For older versions of the firmware updater (before 6.57, you have to manually reset the board for the update to start..
The best way is to use a jumper wire to connect the GND to the reset-pad (TP2):
This however is not needed when you use the UEUpdater on version 6.57
After this it should start uploading the binaries to the module.
It is important to note that for uploading B656 you need CodeLoader v220.127.116.11687 (while B655SP2 needs v18.104.22.168779).
For version 6.57 you can use the UEUpdater and firmware as is described in the main NB-IoT updater page.