cellular-at-modem-integration

# Cellular AT Modem Integration ## Overview Use this skill to drive a 2G/4G/NB-IoT/LTE-M cellular modem from an MCU over UART with the AT command set. The hard parts are parsing unsolicited result codes (URCs) that interleave with command responses on one serial line, choosing the right registration command per radio access technology, using the correct socket command set for the specific module family, and getting PWRKEY boot timing right before any AT works. ## When To Use Use this skill when: - The user integrates Quectel (`EC25`, `BG96`, `BC66`), SIMCom (`SIM7600`, `SIM800C`, `A7670`), or u-blox (`SARA-R4`, `SARA-R5`) over UART. - The issue involves registration (`AT+CPIN?`, `AT+CSQ`, `AT+CREG?`, `AT+CGREG?`, `AT+CEREG?`), APN/PDP (`AT+CGDCONT`, `AT+CGATT`, `AT+CGACT`), or sockets (`AT+QIOPEN`, `AT+QISEND`, `AT+CIPSTART`/`AT+CIPOPEN`, `AT+USOCO`). - URCs such as `RING`, `+CMTI`, or `+QIURC` corrupt command parsing, or power saving (`AT+CPSMS`, `AT+CEDRXS`) breaks reachability. Do not use this skill when the UART link itself is unproven; confirm the modem echoes `AT` with `OK` at the configured baud first. ## First Questions Ask for: - Exact module and firmware revision (`ATI`, `AT+CGMR`), and radio technology: 2G, LTE Cat-1, Cat-4, Cat-M1, or NB-IoT. - UART wiring: baud, flow control (RTS/CTS), and whether `PWRKEY`/reset lines are MCU-controlled. - SIM type and the operator APN (some IoT SIMs need username/password or a specific `<PDP_type>`). - Transport goal: r...