Interact with nRF9151 using external third party MCU

[bojan]

Hello, guys 

We want to evaluate nRF9151 SiP the following way:

• To set it to operate in serial mode in which it is ready to receive AT commands (it comes pre-flashed in that mode on nRF9151-DK, to the best of my understanding)
• To send AT commands and other necessary GPIO control using some external MCU (not nRF5340 MCU which is populated on nRF9151-DK board but some third party, external MCU)

Few questions related to our goal:

1. Is it possible to achieve what we want?
2. Which UART interface should we use for sending AT commands - UART1 or UART2?
3. In addition to UART Rx/Tx, do we need some other GPIO to control the modem (e.g. Reset, some other GPIO that plays a role in modem control...)?
4. We would like to test NB-IoT modem by default and switch to LTE-M if needed. How to achieve this, is there any special AT command for switching between available modes (NB-IoT/LTE-M)?

Thanks in advance for your time and efforts. Looking forward to hearing from you.

Sincerely,
Bojan.

[Michal]

Which NCS version are you using?

[bojan]

For the SLM app, it was compiled with the latest NCS (v2.7.0). Concerning the external MCU, it is a third party MCU that is running cellular_modem Zephyr sample. 

[Michal]

Sorry for the delay, I was sick and out of office.

I will try it myself possibly tomorrow.

[bojan]

No problem, Michal. Thanks for the info.

[Michal]

Unfortunately in the end I had to be away for the rest of the week as well.

I will test it in the following days.

I have been looking at the sample and while the cellular_modem sample is from zephyr and not NCS, there have been commits for nRF91 support, so there shouldn't be any big incompatibilities.