printertest.ino

#include "Adafruit_Thermal.h"

// Pass addr to printer constructor
Adafruit_Thermal printer(&Serial1);
Adafruit_Thermal printer2(&Serial3);

// -----------------------------------------------------------------------

void setup() {

  Serial1.begin(19200); // Initialize serial with printer baudrate
  Serial3.begin(19200);

  printer.begin();      // Init printer
  printer2.begin();

  /**
   * HOW CAN I MAKE THESE TWO FUNCTIONS EXECUTE
   * RELATIVELY SIMULTANEOUSLY? OR ASYNCHRONOUSLY.
   */
  printer.println(F("Testing printer 1!"));
  printer2.println(F("Testing printer 2!"));

  printer.sleep();      // Tell printer to sleep
  printer2.sleep();     // Tell printer to sleep
  delay(3000L);         // Sleep for 3 seconds
  printer.wake();       // MUST wake() before printing again, even if reset
  printer2.wake();       // MUST wake() before printing again, even if reset
  printer.setDefault(); // Restore printer to defaults
  printer2.setDefault(); // Restore printer to defaults
}

void loop() {
}