Suggestion for Library: LiquidCrystal

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);*
  * }*
  }
  [/font]