This is a modified version of TextLCD on the Cookbook for 20X4 LCD specific. This does not control RW line, so we can reduce the number of pin usage on the mbed.
TextLCD_20X4.cpp
- Committer:
- ym1784
- Date:
- 2010-05-14
- Revision:
- 0:f84245f91a5a
File content as of revision 0:f84245f91a5a:
/* mbed TextLCD Library * Copyright (c) 2007-2009 sford * Released under the MIT License: http://mbed.org/license/mit * * TODO: Needs serious rework/neatening up! */ /* * 2010/05/14 modified for 20X4 LCD by ym1784 */ #include "TextLCD_20X4.h" #include "mbed.h" #include "error.h" using namespace mbed; /* * useful info found at http://www.a-netz.de/lcd.en.php * * * Initialization * ============== * * After attaching the supply voltage/after a reset, the display needs to be brought in to a defined state * * - wait approximately 15 ms so the display is ready to execute commands * - Execute the command 0x30 ("Display Settings") three times (wait 1,64ms after each command, the busy flag cannot be queried now). * - The display is in 8 bit mode, so if you have only connected 4 data pins you should only transmit the higher nibble of each command. * - If you want to use the 4 bit mode, now you can execute the command to switch over to this mode now. * - Execute the "clear display" command * * Timing * ====== * * Nearly all commands transmitted to the display need 40us for execution. * Exceptions are the commands "Clear Display and Reset" and "Set Cursor to Start Position" * These commands need 1.64ms for execution. These timings are valid for all displays working with an * internal clock of 250kHz. But I do not know any displays that use other frequencies. Any time you * can use the busy flag to test if the display is ready to accept the next command. * * _e is kept high apart from calling clock * _rw is kept 0 (write) apart from actions that uyse it differently * -> on this program, the _rw is not used ... ym1784 * _rs is set by the data/command writes */ TextLCD_20X4::TextLCD_20X4(PinName rs, PinName e, PinName d0, PinName d1, PinName d2, PinName d3, int columns, int rows) : _rs(rs), _e(e), _d(d0, d1, d2, d3), _columns(columns), _rows(rows) { _rows = 4; _columns = 20; // Mon, 27 Apr 2009 23:32:34 +0200 // Kevin Konradt: // When using a LCD with 1 row x 16 characters // instead of 2x16, try changing _columns to 8. // (display seems to split the 16 characters into // 2 virtual rows with 8 characters each.) // // 2010/05/14 ym1784 // This program is only for 4 rows x 20 characters specific // _rw = 0; // on this program, the _rw is not used ... ym1784 _e = 1; _rs = 0; // command mode // Should theoretically wait 15ms, but most things will be powered up pre-reset // so i'll disable that for the minute. If implemented, could wait 15ms post reset // instead wait(0.015); // for safety ... ym1784 // send "Display Settings" 3 times (Only top nibble of 0x30 as we've got 4-bit bus) for(int i=0; i<3; i++) { writeNibble(0x3); wait(0.00164); // this command takes 1.64ms, so wait for it } writeNibble(0x2); // 4-bit mode writeCommand(0x28); // Function set 001 BW N F - - writeCommand(0x0C); writeCommand(0x6); // Cursor Direction and Display Shift : 0000 01 CD S (CD 0-left, 1-right S(hift) 0-no, 1-yes cls(); } int TextLCD_20X4::_putc(int value) { if(value == '\n') { newline(); } else { writeData(value); } return value; } int TextLCD_20X4::_getc() { return 0; } void TextLCD_20X4::newline() { _column = 0; _row++; if(_row >= _rows) { _row = 0; } locate(_column, _row); } void TextLCD_20X4::locate(int column, int row) { if(column < 0 || column >= _columns || row < 0 || row >= _rows) { error("locate(%d,%d) out of range on %dx%d display", column, row, _columns, _rows); return; } _row = row; _column = column; // modified for 20X4 LCD switch (_row) { case (0) : address = 0x80 + _column; break; case (1) : address = 0xc0 + _column; break; case (2) : address = 0x94 + _column; break; case (3) : address = 0xd4 + _column; break; } // switch writeCommand(address); } void TextLCD_20X4::cls() { writeCommand(0x01); // Clear Display wait(0.00164f); // This command takes 1.64 ms // locate(0, 0); // We don't have to do this here } void TextLCD_20X4::reset() { cls(); } void TextLCD_20X4::clock() { wait(0.000040f); _e = 0; wait(0.000040f); // most instructions take 40us _e = 1; } void TextLCD_20X4::writeNibble(int value) { _d = value; clock(); } void TextLCD_20X4::writeByte(int value) { writeNibble(value >> 4); writeNibble(value >> 0); } void TextLCD_20X4::writeCommand(int command) { _rs = 0; writeByte(command); } void TextLCD_20X4::writeData(int data) { _rs = 1; writeByte(data); _column++; if(_column >= _columns) { newline(); } }