Board configuration

Arduino MKR GSM 1400

GSM 1400 board defines SerialGSM serial and GSM_DTR, GSM_RESETN pins that are used to control the GSM module:

#define SerialAT SerialGSM
...
void setup() {
  ...
  SerialAT.begin(115200);

  pinMode(GSM_DTR, OUTPUT);
  digitalWrite(GSM_DTR, LOW);
  delay(5);

  // Turn on the GSM module by triggering GSM_RESETN pin
  pinMode(GSM_RESETN, OUTPUT);
  digitalWrite(GSM_RESETN, HIGH);
  delay(100);
  digitalWrite(GSM_RESETN, LOW);
}

Industruino GSM / GPRS Module

Industruino GSM allows selecting Serial1 or Serial with an on-board jumper. Pin 6 is used to turn it on and off.

// Select Serial1 or Serial depending on your module configuration
#define SerialAT Serial1
...
void setup() {
  ...
  SerialAT.begin(115200);

  // Turn on the GSM module with 1 second pulse on pin 6
  pinMode(6, OUTPUT);
  digitalWrite(6, HIGH);
  delay(1000);
  digitalWrite(6, LOW);
}

Hologram Dash

Hologram Dash communicates with the GSM module via System microcontroller. Interestingly, it supports the Passthrough mode, that allows communicating with the GSM module directly:

#define SerialAT SerialSystem
...
void setup() {
  ...
  // Set up Passthrough
  HologramCloud.enterPassthrough();
}