Adafruit Motor Shield v2, two motors, on an Arduino Uno

// Two DC motors on the Adafruit Motor Shield v2.
//
// The shield's PCA9685 sits at I2C address 0x60 and drives all four bridges
// of its two TB6612s, so the Uno spends only SDA and SCL on four motors.
// Motor power goes on VIN+ and VIN-.

#include <Wire.h>
#include <Adafruit_MotorShield.h>

Adafruit_MotorShield shield;
Adafruit_DCMotor *m1 = shield.getMotor(1);
Adafruit_DCMotor *m2 = shield.getMotor(2);

void setup() {
  Serial.begin(9600);
  if (!shield.begin()) Serial.println("No motor shield at 0x60");
  m1->setSpeed(200);
  m2->setSpeed(200);
}

void loop() {
  m1->run(FORWARD);
  m2->run(BACKWARD);
  delay(1500);
  m1->run(RELEASE);
  m2->run(RELEASE);
  delay(500);
  m1->run(BACKWARD);
  m2->run(FORWARD);
  delay(1500);
  m1->run(RELEASE);
  m2->run(RELEASE);
  delay(500);
}