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Hello, Massimo;

Since you've made LiquidCrystal part of standard libraries beginning with 0012 - I have a suggestion:

LiquidCrystal can use 4 or 8 bit mode;
and will utilize the following LCD module pins:
4 bit: RW, EN, RS, D4, D5, D6, D7
8 bit: RW, EN, RS, D0, D1, D4, D3, D4, D5, D6, D7

However, in many cases there is no need to use 7/11 pins for 4/8 bit LCD control mode; instead, RW pin of LCD can be hard wired to GND, to save 1 Arduino pin for purposes other then LCD; thus LCD will consume 6/10 pins total.

I propose to use "-1" value for RW in LiquidCrystal constructor to tell this library to ignore / do not use this pin.

Proposed code comes below;

Cheers.



++++++++++++++++++++++++++++++


#include "LiquidCrystal.h"

#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include "WProgram.h"

// When the display powers up, it is configured as follows:
//
// 1. Display clear
// 2. Function set:
//    DL = 1; 8-bit interface data
//    N = 0; 1-line display
//    F = 0; 5x8 dot character font
// 3. Display on/off control:
//    D = 0; Display off
//    C = 0; Cursor off
//    B = 0; Blinking off
// 4. Entry mode set:
//    I/D = 1; Increment by 1
//    S = 0; No shift
//
// Note, however, that resetting the Arduino doesn't reset the LCD, so we
// can't assume that its in that state when a sketch starts (and the
// LiquidCrystal constructor is called).

//      set rw = -1, if pin should not be used by arduino
//      in this case hard wire rw pin of LCD module to GND.

LiquidCrystal::LiquidCrystal(uint8_t rs, uint8_t rw, uint8_t enable,
            uint8_t d0, uint8_t d1, uint8_t d2, uint8_t d3, uint8_t d4, uint8_t d5,
            uint8_t d6, uint8_t d7) :
      _four_bit_mode(0), _rs_pin(rs), _rw_pin(rw), _enable_pin(enable) {
      _data_pins[0] = d0;
      _data_pins[1] = d1;
      _data_pins[2] = d2;
      _data_pins[3] = d3;
      _data_pins[4] = d4;
      _data_pins[5] = d5;
      _data_pins[6] = d6;
      _data_pins[7] = d7;

      pinMode(_enable_pin, OUTPUT);
      pinMode(_rs_pin, OUTPUT);

      if (_rw_pin >= 0) { // "do not use rw" indicated by rw = -1
            pinMode(_rw_pin, OUTPUT);
      }

      for (int i = 0; i < 8; i++)
            pinMode(_data_pins, OUTPUT);

      command(0x38); // function set: 8 bits, 1 line, 5x8 dots
      command(0x0C); // display control: turn display on, cursor off, no blinking
      command(0x06); // entry mode set: increment automatically, display shift, right shift

      clear();

}

LiquidCrystal::LiquidCrystal(uint8_t rs, uint8_t rw, uint8_t enable,
            uint8_t d0, uint8_t d1, uint8_t d2, uint8_t d3) :
      _four_bit_mode(1), _rs_pin(rs), _rw_pin(rw), _enable_pin(enable) {
      _data_pins[0] = d0;
      _data_pins[1] = d1;
      _data_pins[2] = d2;
      _data_pins[3] = d3;

      pinMode(_enable_pin, OUTPUT);
      pinMode(_rs_pin, OUTPUT);

      if (_rw_pin >= 0) { // "do not use rw" indicated by rw = -1
            pinMode(_rw_pin, OUTPUT);
      }

      for (int i = 0; i < 4; i++)
            pinMode(_data_pins, OUTPUT);

      command(0x28); // function set: 4 bits, 1 line, 5x8 dots
      command(0x0C); // display control: turn display on, cursor off, no blinking
      command(0x06); // entry mode set: increment automatically, display shift, right shift

      clear();

}

void LiquidCrystal::clear() {
      command(0x01); // clear display, set cursor position to zero
      delayMicroseconds(2000);
}

void LiquidCrystal::home() {
      command(0x02); // set cursor position to zero
      delayMicroseconds(2000);
}

void LiquidCrystal::setCursor(int col, int row) {
      int row_offsets[] = { 0x00, 0x40, 0x14, 0x54 };
      command(0x80 | (col + row_offsets[row]));
}

void LiquidCrystal::command(uint8_t value) {
      send(value, LOW);
}

void LiquidCrystal::write(uint8_t value) {
      send(value, HIGH);
}

void LiquidCrystal::send(uint8_t value, uint8_t mode) {

      digitalWrite(_rs_pin, mode);

      if (_rw_pin >= 0) { // "do not use rw" indicated by rw = -1
            digitalWrite(_rw_pin, LOW);
      }

      if (_four_bit_mode) {
            for (int i = 0; i < 4; i++) {
                  digitalWrite(_data_pins, (value >> (i + 4)) & 0x01);
            }

            digitalWrite(_enable_pin, HIGH);
            digitalWrite(_enable_pin, LOW);

            for (int i = 0; i < 4; i++) {
                  digitalWrite(_data_pins, (value >> i) & 0x01);
            }

            digitalWrite(_enable_pin, HIGH);
            digitalWrite(_enable_pin, LOW);
      } else {
            for (int i = 0; i < 8; i++) {
                  digitalWrite(_data_pins, (value >> i) & 0x01);
            }

            digitalWrite(_enable_pin, HIGH);
            digitalWrite(_enable_pin, LOW);
      }
}