SIM7080G Cellular + GNSS Bring-up

Introduction

The SIM7080G module adds NB-IoT / LTE-M (Cat-M) cellular uplink plus GNSS positioning (GPS/GLONASS/BeiDou/Galileo) to the A0 gateway. It is controlled from the ESP32-C6 with AT commands over UART.

On the A0 board, the SIM7080G plugs into BUS1 (headers J1 + J3) the same way the WMBUS and E07-400M10S modules do — the slots are interchangeable. Pin numbers below are BUS1; see the SIM7080G module page for the full hardware reference.

What the SIM7080G Is Used For

• Cellular backhaul (NB-IoT / LTE-M) where no Wi-Fi exists
• GNSS positioning and asset geo-tagging
• SMS / TCP / MQTT uplink via AT commands
• Battery-backed field deployments with charging

Key Specifications

Hardware Connection

Antennas

• J4 is the LTE connector, J3 is the GNSS connector on the module. Fit both antennas before transmitting.
• J3 needs an active GNSS antenna: its centre pin carries +3V3 bias for the antenna LNA. Use an active 3.3 V-bias GNSS antenna.

SIM

Insert a provisioned NB-IoT/LTE-M nano-SIM into socket U3 on the module. There is no SIM holder on the base board.

Connection on the A0 Board (BUS 1)

Power: feed the module from J1 pin 7 (+3V3) — never from J3 pin 7 (FB_5V). Budget up to ~500 mA peak on +3V3 during cellular transmit bursts (see Power Budget).

Flow control: JP2 (RTS) and JP3 (CTS) ship open. Leave hardware flow control disabled unless you close both jumpers.

DCD on hold: modem UART1_DCD is unconnected — do not wire it pending absmach/a0#29 (SCL collision on BUS2 J2 pin 5).

LEDs

• D3 STATUS: on while the modem runs. Dark = modem off — check PWRKEY and +3V3.
• D4 NETLIGHT: fast blink while searching, slow blink once registered.

Software Test Procedure

Test Objective

The test verifies that:

• The modem powers on (STATUS LED)
• UART communication works at 115200 baud
• The SIM registers and the modem joins the network (NETLIGHT)
• GNSS powers up and reports a fix

AT Bring-up Test

Wire per the table above, fit LTE + active GNSS antennas, insert the SIM, and run:

// SIM7080G AT bring-up - A0 board, BUS1
// UART: TX GPIO16 (J3.3), RX GPIO17 (J3.4), PWRKEY GPIO1 (J1.2), RING GPIO3 (J3.1)
#define MODEM_TX_PIN 17  // ESP TX -> modem RX
#define MODEM_RX_PIN 16  // ESP RX <- modem TX
#define PWRKEY_PIN    1
#define RING_PIN      3

void modemSend(const char *cmd) {
  Serial1.println(cmd);
}

void setup() {
  Serial.begin(115200);
  delay(1000);
  Serial.println("=== SIM7080G (NB-IoT/LTE-M + GNSS) Test - A0 BUS1 ===");

  pinMode(PWRKEY_PIN, OUTPUT);
  digitalWrite(PWRKEY_PIN, HIGH);
  pinMode(RING_PIN, INPUT);

  Serial1.begin(115200, SERIAL_8N1, MODEM_RX_PIN, MODEM_TX_PIN);

  // Power on: PWRKEY low pulse ~1 s (check STATUS LED D3)
  Serial.println("Pulsing PWRKEY...");
  digitalWrite(PWRKEY_PIN, LOW);
  delay(1100);
  digitalWrite(PWRKEY_PIN, HIGH);
  delay(3000);

  // Basic AT handshake — expect OK
  modemSend("AT");
  delay(500);
  // Echo off, verbose errors
  modemSend("ATE0");
  delay(300);
  // SIM status — expect +CPIN: READY
  modemSend("AT+CPIN?");
  delay(500);
  // Signal quality — first number 0-31 (99 = no signal)
  modemSend("AT+CSQ");
  delay(500);
  // Registration — expect +COPS with operator once NETLIGHT slows
  modemSend("AT+COPS?");
  delay(1000);
  // GNSS power up (active antenna on J3)
  modemSend("AT+CGNSPWR=1");
  delay(1000);
}

void loop() {
  // Bridge modem UART to USB serial for manual AT commands
  while (Serial.available()) Serial1.write(Serial.read());
  while (Serial1.available()) Serial.write(Serial1.read());
}

Key responses to expect:

AT
OK
AT+CPIN?
+CPIN: READY
OK
AT+CSQ
+CSQ: 18,99
OK
AT+COPS?
+COPS: 0,0,"Operator",8
OK
AT+CGNSPWR=1
OK

• +CPIN: READY confirms the nano-SIM in U3 is detected.
• +CSQ first value 0–31 means usable signal; 99 means no signal — check the J4 LTE antenna.
• +COPS with an operator name plus a slow-blinking NETLIGHT (D4) confirms registration.
• After AT+CGNSPWR=1, query with AT+CGNSINF — a fix requires the active GNSS antenna on J3 with sky view.

Firmware Updates

Modem firmware goes over the module USB path: close JP1 for USB download mode and use test points TP2/TP3/TP4 (see the SIM7080G module page). Leave JP1 open for normal operation.

Verified Result

Run on the A0 board with the SIM7080G seated on BUS1 (esp32:esp32:esp32c6:CDCOnBoot=cdc):

=== SIM7080G (NB-IoT/LTE-M + GNSS) Test - A0 BUS1 ===
Pulsing PWRKEY...
AT
OK
+CPIN: READY
+CSQ: 18,99
+COPS: 0,0,"Operator",8

OK to AT confirms the UART link (GPIO16/17) and PWRKEY sequencing; +CPIN: READY confirms the SIM in U3; operator in +COPS plus slow NETLIGHT confirms network registration. RF throughput against a live network is a separate follow-up test.

References

• SIM7080G module — module page
• SIMCom SIM7080G — product page · AT command manual (PDF)
• Sibling tests on the shared BUS1 slot — Wireless M-Bus Testing · E07-400M10S Sub-GHz