Title:
Hi,
We want to use the nRF9151 as an external LTE modem, controlled from another MCU through UART AT commands.
We have designed our own PCB with the nRF9151. For the first bring-up, we are loading the firmware using the nRF Connect for Desktop app, following the Quick Start flow and selecting/loading the Serial Modem firmware. We program the custom board through JTAG/SWD using a Nordic development kit as the debugger. We are trying to communicate with the PC connecting to the UART pins.
nRF9151 TX -> external host RX
nRF9151 RX <- external host TX
nRF9151 CTS -> forced LOW
nRF9151 RTS -> currently not controlled
DTR -> HIGH
VDD_GPIO -> 3.3 V
GND -> common ground
When we reset the board, we can receive the following logs through UART:
All pins have been configured as non-secure
Booting TF-M v2.1.1-ncs4
[Sec Thread] Secure image initializing!
TF-M isolation level is: 0x00000001
TF-M Float ABI: Hard
Lazy stacking enabled
So it seems that the nRF9151 is booting and at least the TX path from the nRF9151 to the host is working.
However, after that, the device does not respond to AT commands. We are sending:
AT\r
but we do not receive OK.
My questions are:
-
Is it correct to load the Serial Modem firmware into a custom nRF9151 board using the nRF Connect for Desktop Quick Start flow and a Nordic development kit as JTAG/SWD debugger?
-
Is this the recommended approach for first bring-up, or is there another preferred method to program Serial Modem on a custom board?
-
If we need to customize UART pins, DTR/RI behavior, flow control, or external flash configuration, do we need to download the SDK and the Serial Modem project, modify the devicetree overlay, rebuild the image in VS Code / west, and then flash the generated image?
-
Since we can see TF-M boot logs but no AT response, what are the most likely causes?
Any guidance on the recommended workflow for using Serial Modem on a custom nRF9151 board would be appreciated.
Best regards.
