Twenty by four on an Arduino Uno

// Twenty by four: two 20x4 character LCDs, one on six wires and one on two.
//
//   bare 20x4   RS -> 2   E -> 3   D4..D7 -> 4, 5, 6, 7
//               VSS, V0, RW -> GND    VDD -> 5 V
//   I2C 20x4    SDA -> A4   SCL -> A5   VCC -> 5 V   GND -> GND
//
// A 20x4 is the same HD44780 controller as a 16x2, and the controller only has
// two lines of memory, forty characters each. The panel shows each line twice
// over: row 0 is the first twenty characters of line 1 and row 2 the next
// twenty, rows 1 and 3 the same of line 2. So the rows start at 0x00, 0x40,
// 0x14 and 0x54, and setCursor() knows that.
//
// The bare panel shows what happens without it: one long print runs off the
// end of row 0 and carries on in row 2, not row 1. The I2C panel counts, with
// each row placed by setCursor().

#include "mokxi_lcd1602.h"
#include "mokxi_lcd1602_i2c.h"

Lcd1602 bare(2, 3, 4, 5, 6, 7);
Lcd1602I2c backpack(A5, A4);

void setup() {
  bare.begin();
  // Forty characters in one go: the second twenty land in row 2.
  bare.print("Row 0 runs off here ");
  bare.print("and on into row 2...");
  bare.setCursor(0, 1);
  bare.print("Row 1 is line 2");

  backpack.begin();
  backpack.setCursor(0, 0);
  backpack.print("Twenty by four");
  backpack.setCursor(0, 1);
  backpack.print("rows at 00 40 14 54");
  backpack.setCursor(0, 2);
  backpack.print("seconds:");
}

void loop() {
  backpack.setCursor(9, 2);
  backpack.print((long)(millis() / 1000));
  backpack.setCursor(0, 3);
  backpack.print("row 3 is 0x54");
  delay(250);
}