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LiquidCrystal_I2C.cpp
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LiquidCrystal_I2C.cpp
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/*
* © 2021, Neil McKechnie. All rights reserved.
* Based on the work by DFRobot, Frank de Brabander and Marco Schwartz.
*
* This file is part of CommandStation-EX
*
* This is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* It is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with CommandStation-EX. If not, see <https://www.gnu.org/licenses/>.
*/
#include <Arduino.h>
#include "LiquidCrystal_I2C.h"
#include "DIAG.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).
LiquidCrystal_I2C::LiquidCrystal_I2C(I2CAddress lcd_Addr, uint8_t lcd_cols,
uint8_t lcd_rows) {
_Addr = lcd_Addr;
lcdRows = lcd_rows; // Number of character rows (typically 2 or 4).
lcdCols = lcd_cols; // Number of character columns (typically 16 or 20)
_backlightval = 0;
}
bool LiquidCrystal_I2C::begin() {
I2CManager.begin();
I2CManager.setClock(100000L); // PCF8574 is spec'd to 100kHz.
if (I2CManager.exists(_Addr)) {
DIAG(F("%dx%d LCD configured on I2C:%s"), (int)lcdCols, (int)lcdRows, _Addr.toString());
_displayfunction = LCD_4BITMODE | LCD_1LINE | LCD_5x8DOTS;
backlight();
} else {
DIAG(F("LCD not found on I2C:%s"), _Addr.toString());
return false;
}
if (lcdRows > 1) {
_displayfunction |= LCD_2LINE;
}
// according to datasheet, we need at least 40ms after power rises above 2.7V
// before sending commands. Arduino can turn on way before 4.5V so we'll allow
// 100 milliseconds after pulling both RS and R/W and backlight pin low
expanderWrite(
_backlightval); // reset expander and turn backlight off (Bit 8 =1)
delay(100);
// put the LCD into 4 bit mode
// this is according to the hitachi HD44780 datasheet
// figure 24, pg 46
// we start in 8bit mode, try to set 4 bit mode
write4bits(0x03);
delayMicroseconds(5000); // wait min 4.1ms
// second try
write4bits(0x03);
delayMicroseconds(5000); // wait min 4.1ms
// third go!
write4bits(0x03);
delayMicroseconds(5000);
// finally, set to 4-bit interface
write4bits(0x02);
// set # lines, font size, etc.
command(LCD_FUNCTIONSET | _displayfunction);
// turn the display on with no cursor or blinking default
_displaycontrol = LCD_DISPLAYON | LCD_CURSOROFF | LCD_BLINKOFF;
display();
// Initialize to default text direction (for roman languages)
_displaymode = LCD_ENTRYLEFT | LCD_ENTRYSHIFTDECREMENT;
// set the entry mode
command(LCD_ENTRYMODESET | _displaymode);
return true;
}
/********** high level commands, for the user! */
void LiquidCrystal_I2C::clearNative() {
command(LCD_CLEARDISPLAY); // clear display, set cursor position to zero
delayMicroseconds(2000); // this command takes 1.52ms but allow plenty
}
void LiquidCrystal_I2C::setRowNative(byte row) {
uint8_t row_offsets[] = {0x00, 0x40, 0x14, 0x54};
if (row >= lcdRows) {
row = lcdRows - 1; // we count rows starting w/0
}
command(LCD_SETDDRAMADDR | (row_offsets[row]));
}
void LiquidCrystal_I2C::display() {
_displaycontrol |= LCD_DISPLAYON;
command(LCD_DISPLAYCONTROL | _displaycontrol);
}
// Turn the (optional) backlight off/on
void LiquidCrystal_I2C::noBacklight(void) {
_backlightval &= ~LCD_BACKLIGHT;
expanderWrite(0);
}
void LiquidCrystal_I2C::backlight(void) {
_backlightval = LCD_BACKLIGHT;
expanderWrite(0);
}
size_t LiquidCrystal_I2C::writeNative(uint8_t value) {
send(value, Rs);
return 1;
}
bool LiquidCrystal_I2C::isBusy() {
return rb.isBusy();
}
/*********** mid level commands, for sending data/cmds */
inline void LiquidCrystal_I2C::command(uint8_t value) {
send(value, 0);
}
/************ low level data pushing commands **********/
/* According to the NXP Datasheet for the PCF8574 section 8.2:
* "The master (microcontroller) sends the START condition and slave address
* setting the last bit of the address byte to logic 0 for the write mode.
* The PCF8574/74A acknowledges and the master then sends the data byte for
* P7 to P0 to the port register. As the clock line goes HIGH, the 8-bit
* data is presented on the port lines after it has been acknowledged by the
* PCF8574/74A. [...] The master can then send a STOP or ReSTART condition
* or continue sending data. The number of data bytes that can be sent
* successively is not limited and the previous data is overwritten every
* time a data byte has been sent and acknowledged."
*
* This driver takes advantage of this by sending multiple data bytes in succession
* within a single I2C transmission. With a fast clock rate of 400kHz, the time
* between successive updates of the PCF8574 outputs will be at least 2.5us. With
* the default clock rate of 100kHz the time between updates will be at least 10us.
*
* The LCD controller HD44780, according to its datasheet, needs nominally 37us
* (up to 50us) to execute a command (i.e. write to gdram, reposition, etc.). Each
* command is sent in a separate I2C transmission here. The time taken to end a
* transmission and start another one is a stop bit, a start bit, 8 address bits,
* an ack, 8 data bits and another ack; this is at least 20 bits, i.e. >50us
* at 400kHz and >200us at 100kHz. Therefore, we don't need additional delay.
*
* Similarly, the Enable must be set/reset for at least 450ns. This is
* well within the I2C clock cycle time of 2.5us at 400kHz. Data is clocked in
* to the HD44780 on the trailing edge of the Enable pin, so we set the Enable
* as we present the data, then in the next byte we reset Enable without changing
* the data.
*/
// write either command or data (8 bits) to the HD44780 LCD controller as
// a single I2C transmission.
void LiquidCrystal_I2C::send(uint8_t value, uint8_t mode) {
mode |= _backlightval;
uint8_t highnib = (((value >> 4) & 0x0f) << BACKPACK_DATA_BITS) | mode;
uint8_t lownib = ((value & 0x0f) << BACKPACK_DATA_BITS) | mode;
// Send both nibbles
uint8_t len = 0;
rb.wait();
outputBuffer[len++] = highnib|En;
outputBuffer[len++] = highnib;
outputBuffer[len++] = lownib|En;
outputBuffer[len++] = lownib;
I2CManager.write(_Addr, outputBuffer, len, &rb); // Write command asynchronously
}
// write 4 data bits to the HD44780 LCD controller.
void LiquidCrystal_I2C::write4bits(uint8_t value) {
uint8_t _data = ((value & 0x0f) << BACKPACK_DATA_BITS) | _backlightval;
// Enable must be set/reset for at least 450ns. This is well within the
// I2C clock cycle time of 2.5us at 400kHz. Data is clocked in to the
// HD44780 on the trailing edge of the Enable pin.
uint8_t len = 0;
rb.wait();
outputBuffer[len++] = _data|En;
outputBuffer[len++] = _data;
I2CManager.write(_Addr, outputBuffer, len, &rb); // Write command asynchronously
}
// write a byte to the PCF8574 I2C interface. We don't need to set
// the enable pin for this.
void LiquidCrystal_I2C::expanderWrite(uint8_t value) {
rb.wait();
outputBuffer[0] = value | _backlightval;
I2CManager.write(_Addr, outputBuffer, 1, &rb); // Write command asynchronously
}