LCD driver
As a gift for putting you through revamping my site, here are the particulars for an LCD serial driver that I personally use in projects and used to sell commercially.
The SLD01a serial LCD driver design is a for a Microchip PIC 16F628a, but it should be simple to port over to any PIC with a USART. It converts serial data in either RS-232c or TTL formats to display on any Hitachi HD44780-compatible LCD. Applications include industrial/PLC control read-outs, microprocessor projects, computer mods, and anything else that uses serial data. It doesn’t have a lot of bells and whistles (but it DOES have a bell DRIVER) as some other drivers do. It’s designed to be a simple, light-weight terminal-style display.
To paraphrase the documentation sheet:
The SLD01a serial LCD driver will convert raw serial data into a 4-bit parallel format applicable to LCD displays which use a Hitachi HD44780-compatible character display chipset. A 64 byte receive buffer is used to assist in data loss prevention.
The SLD01a requires a 5vdc powersupply. Additional support circuitry is necessary to convert RS232C data signals to TTL if the SLD01a is intended for this purpose. A MAX232 or similar is typically all that is required, as shown in the sample schematic.
Serial data must be in format: 8-bit, no parity, 1 stop bit, and at the rate of 9600 bps. Any other settings will require editing the provided source.
When the non-text linefeed and carriage return characters are received the SLD01a will cause the LCD display cursor to move to the first character placement on the next line of the display. After the last character of the last line is reached the SLD01a will clear the display and begin again at the first character of the first line.
When the non-printable delete character is encountered, the SLD01a will delete the last displayed character.
When the non-printable ASCII bell character 7 (0×07) is encountered the aux pin (6) will energize briefly. this is the same as the ‘b’ escape sequence.
Some proprietary escape sequences allow for some additional features. Escape sequences begin with the ASCII escape character 27 (0x1b) The table in sheet 3 below lists the escape sequences recognized by the SLD01a and the functions that they perform.
The LCD can be configured for specific numbers of columns and lines with two additional escape sequences. The desired number of columns is set by first sending the escape character, then a lower-case ‘x’, followed by two digits to specify the number of columns allowed before the SLD01a forces a line-break. The LCD line count is specifed in a similar manner – ecsape + lower-case ‘y’ + two digits. For example, to set the SLD01a to format in 16 x 2 mode you would send “\x16\y02″, (with the backslash representing the escape character) LCD configurations are saved in the SLD01a EEPROM which is persistant even when powered down. This makes it only necessary to configure the SLD01a the first time it is matched to any given LCD.
Sheet 1: Sample schematic using an interface chip
Sheet 2: Sample wiring diagram using an interface chip
Sheet 3: Documentation
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#include "C:\Program Files\bknd\CC5X\16F628A.H" // target pic
#include "C:\Program Files\bknd\CC5X\INT16CXX.H" // interrupt routines
#pragma config &= ~0b11.1111.1111.1111 // clear all
#pragma config |= 0b11.1111.0001.1000
// --.----.---*.--** FOSC = IRCIO (1--00)
// --.----.----.-*-- WDTE disabled
// --.----.----.*--- power up timer PWRTE disabled
// --.----.--*-.---- MCLRE: RA5 is IO, MCLRE disabled
// --.----.-*--.---- BOREN: brown out detect disabled
// --.----.*---.---- LVP: low voltage programming diasabled (makes RB4 free)
// -*.****.*---.---- UNUSED: must be 1's
// *-.----.----.---- CP: code protect off
#pragma bit LCD_RS @ PORTA.3 // LCD Register Select (1=data, 0=instruction)
#pragma bit LCD_EN @ PORTA.2 // LCD Enable LCD latches data at H->L transition
#pragma bit LCD_D4 @ PORTA.6 // LCD data pin 4
#pragma bit LCD_D5 @ PORTA.7 // LCD data pin 5
#pragma bit LCD_D6 @ PORTA.0 // LCD data pin 6
#pragma bit LCD_D7 @ PORTA.1 // LCD data pin 7
#pragma bit BELL_PIN @ PORTB.0 // bell output
#pragma bit LED_PIN @ PORTB.3 // LCD backlight
#define TRUE 1
#define FALSE 0
#define BELL_CYCLES 7500 // number of cycles to hold bell on
#define CHR_BEL 7 // bell char
#define CHR_DEL 8 // backspace char
#define CHR_LF 10 // linefeed char
#define CHR_CR 13 // carriage return char
#define CHR_ESC 27 // escape char
#define CMD_CLEAR 0b.0000.0001 // clear LCD
#define CMD_HOME 0b.0000.0010 // Move cursor home position
#define CMD_LEFT 0b.0001.0000 // Move cursor one to left
#define CMD_MOV 0b.1000.0000 // CMD_MOV + X: Sets cursor position to X
#define CMD_LF 0b.1100.0000 // 2nd line (not an actual LF - will not work on 20x4 displays!)
bit rcv; // bool to esc during startup
bit bell_flag;
bit bell_latch;
uns16 bell_count; // current count of bell flag cycles
#pragma rambank 1
uns8 buffer[64]; // buffer
#pragma rambank 0
uns8 buf_w_pos; // buffer write cursor position
uns8 buf_r_pos; // buffer read cursor position
uns8 buf_sz; // buffer size
uns8 data_byte;
uns8 N_COL; // column count
uns8 N_LIN; // line count
uns8 LIN_ADR[4]; // array of lines
uns8 POS_COL; // column position
uns8 POS_LIN; // line position
// ----------------------------
// interrupt service routine
// ----------------------------
#pragma origin 4 // mandatory when interrupts are used
interrupt isr(void) {
int_save_registers
char save_FSR = FSR;
while (RCIF) { // set when receive register is loaded
// append to buffer and increase size
data_byte = RCREG; // clears RSR serial buffer
buffer[buf_w_pos] = data_byte;
buf_w_pos++;
if (buf_w_pos > 63) {
buf_w_pos = 0;
}
buf_sz++;
if (buf_sz > 63) {
buf_sz = 63;
}
if (OERR == 1) { // overrun error flag, toggle CREN to clear
CREN = 0;
CREN = 1;
}
}
FSR = save_FSR;
int_restore_registers
}
uns8 bin2Hex(char x) {
skip(x);
#pragma return[16] = "0123456789ABCDEF"
}
// -------------------------------------------------------
// initialize pic registers
// -------------------------------------------------------
static void initPIC() {
CMCON = 0b0000.0111; // Comparator off
CCP1CON = 0b0000.0000; // Capt/Comp/PWM off
PORTA = 0b0000.0000; // all ports zero
TRISA = 0b0000.0000; // 0 = Output, 1 = Input
// ---*.---- PORTA.5 is PB_ENTER
PORTB = 0b0000.0000; // all ports zero
TRISB = 0b0000.0010; // 0 = Output, 1 = Input... IN: RB1/RX, RB2/TX(?)
// (value from table 12-5 on page 72 of 16F62x datasheet)void enable_uart_RX(bit want_ints)
SPBRG = 25; //IRCIO 4mHz 9600 Baud async mode
TXSTA = 0b0000.0100; // transmit status and control
// ----.---* TX9D: 9th bit of transmit data. Can be parity
// ----.--*- TRMT: Transmit Shift Register Status
// ----.-*-- BRGH: High Baud Rate Select -- 0 = low, 1 = high
// ----.*--- Unimplemented: Read as '0'
// ---*.---- SYNC: USART Mode -- 1 = synchronous, 0 = asynchronous
// --*-.---- TXEN: Transmit Enable
// -*--.---- TX9: 9-bit Transmit Enable -- 1 = 9-bit transmission, 0 = 8-bit transmission
// *---.---- CRSC: clock source -- async: Don’t care / sync: 1 = BRG clock, 0 = ext clock
RCSTA = 0b1001.0000; // receive status and control
// ----.---* RX9D: 9th bit of received data, can be parity bit
// ----.--*- OERR: Overrun Error
// ----.-*-- FERR: Framing Error
// ----.*--- Unimplemented: Read as '0'
// ---*.---- CREN: Continuous Receive -- async: 1 = enabled, 0 = disabled / sync *
// --*-.---- SREN: Single Receive Enable bit -- async: Don’t care / sync master: 1 = enabled, 0 = disabled
// -*--.---- RX9: 9-bit Receive Enable -- 1 = 9-bit reception, 0 = 8-bit reception
// *---.---- SPEN: Serial Port Enable -- 1 = enabled (RX/DT and TX/CK are serial port pins), 0 = disabled
// *: 1 = Enabled until enable bit CREN is cleared (CREN overrides SREN), 0 = Disabled
// enable interrupts for RX buffer
RCIE = 1;
PEIE = 1;
GIE = 1;
LIN_ADR[0] = 0;
LIN_ADR[1] = 64;
LIN_ADR[2] = 32;
LIN_ADR[3] = 96;
}
void delay_ms(uns8 x) {
uns8 y, z;
// couple of for loops to cause a specific delay.
for ( ; x > 0 ; x--)
for ( y = 0 ; y < 4 ; y++)
for ( z = 0 ; z < 136 ; z++);
}
void delay_cycles(uns8 x) {
for ( ; x > 0 ; x--);
}
void writeLCDcmd(uns8 byte) {
// disable interrupts during LCD writes
GIE = 0;
LCD_RS = 0; // cmd sig
//MSB
LCD_D4 = byte.4;
LCD_D5 = byte.5;
LCD_D6 = byte.6;
LCD_D7 = byte.7;
// pulse LCD_EN line...
LCD_EN = 1;
LCD_EN = 0;
//LSB
LCD_D4 = byte.0;
LCD_D5 = byte.1;
LCD_D6 = byte.2;
LCD_D7 = byte.3;
// pulse LCD_EN line...
LCD_EN = 1;
LCD_EN = 0;
// delay while LCD complies
// delay_cycles(180);
delay_cycles(200);
// enable interrupts
GIE = 1;
}
void writeLCDchar(uns8 byte) {
// disable interrupts during LCD writes
GIE = 0;
LCD_RS = 1; // set data sig
//MSB
LCD_D4 = byte.4;
LCD_D5 = byte.5;
LCD_D6 = byte.6;
LCD_D7 = byte.7;
// pulse LCD_EN line...
LCD_EN = 1;
LCD_EN = 0;
//LSB
LCD_D4 = byte.0;
LCD_D5 = byte.1;
LCD_D6 = byte.2;
LCD_D7 = byte.3;
// pulse LCD_EN line...
LCD_EN = 1;
LCD_EN = 0;
// delay while LCD complies
delay_cycles(100);
// enable interrupts
GIE = 1;
}
void LCD_CLS(void) {
writeLCDcmd(CMD_CLEAR);
writeLCDcmd(CMD_MOV + LIN_ADR[0]);
POS_LIN = 1;
POS_COL = 0;
}
void LCD_LF(void) {
POS_LIN++;
if (POS_LIN <= N_LIN) {
writeLCDcmd(CMD_MOV + LIN_ADR[POS_LIN - 1]);
POS_COL = 1;
} else {
LCD_CLS();
}
}
//Sends a given string to the LCD. Will start printing from current cursor position.
void writeLCDstr(const char *instring) {
uns8 x;
for(x = 0; instring[x] != '\0'; x++ ) {
if (instring[x] == '\n') {
LCD_LF();
} else {
writeLCDchar(instring[x]);
}
}
}
void writeLCDdigit(uns8 argByte) {
uns8 y,z;
z = argByte;
y = z / 100;
z = z % 100;
if (y != 0)
writeLCDchar(bin2Hex(y)); //Print 100s
y = z / 10;
z = z % 10;
if (y != 0)
writeLCDchar(bin2Hex(y)); //Print 10s
writeLCDchar(bin2Hex(z)); //Print 1s
}
void initLCD(void)
{ // This goes through Hitachi's recomended powerup sequence to set a display to 4-bit interface
delay_ms(20); // Wait for LCD to power up ( >15ms )
writeLCDcmd(0b.0000.0011); // Set interface to 4 bits
delay_ms(5);
writeLCDcmd(0b.0000.0011); // Set interface to 4 bits
delay_ms(2);
writeLCDcmd(0b.0000.0011); // Set interface to 4 bits
delay_ms(5);
writeLCDcmd(0b.0000.0010); // Set the display to 4 bit interface
delay_ms(5);
writeLCDcmd(0b.0010.1000); // Set the LCD to 4-bit interface and two lines
delay_ms(5);
writeLCDcmd(0b.0000.0110); // Curser moves right, display does not shift
delay_ms(5);
writeLCDcmd(0b.0000.0001); // Clear all DDRAM, set current position to line one column one
delay_ms(5);
writeLCDcmd(0b.0000.1100); // Turn display on, turn cursor off, make cursor not blink
delay_ms(5);
}
void writeEEPROMbyte(uns8 argAdr, uns8 argByt) {
GIE = 0; // disable interrupts - the write seq requires a specific number of cycles or will fail
while (GIE) {
// make sure interrupts are disabled
}
EECON1.2 = 1; // set write enable flag WREN (EECON bit 2)
EEADR = argAdr; // select eeprom address
EEDATA = argByt; // load data register byte
EECON2 = 0x55; // write sequence mystery #1
EECON2 = 0xAA; // write sequence mystery #2
EECON1.1 = 1; // set write trigger WR (EECON bit 1)
while (EECON1.1) {
// wait for WR to be cleared by PIC
}
EECON1.2 = 0; // clear WREN
EEIF = 0; // clear EEIF
GIE = 1; // enable interrupts
}
void readLCDconfig() {
EEADR = 0; // select eeprom address 0 for columns
EECON1.0 = 1; // set read enable flag RD
N_COL = EEDATA;
EEADR = 1; // select eeprom address 2 for lines
EECON1.0 = 1; // set read enable flag RD
N_LIN = EEDATA;
}
void LCD_info(void) {
// start-up msg
LCD_CLS();
writeLCDstr(" SLD01A v1.2\n");
writeLCDstr(" 9600 8N1 ");
writeLCDdigit(N_COL);
writeLCDstr("x");
writeLCDdigit(N_LIN);
delay_ms(1000);
}
extern void main(void) {
uns8 cur_byte = '\0';
bit escaped = 0;
uns8 esc_val; // stored escape value
uns8 esc_len; // length of captured escape sequence
uns8 esc_seq = 0;
// ESCAPE SEQUENCES:
// 0 = none designated yet
// 1 = setting LCD columns
// 2 = setting LCD lines
rcv = 0;
// disable interrupts during start-up
GIE = 0;
initPIC();
initLCD();
// read LCD config from EEPROM, default to 16 * 2
readLCDconfig();
if (N_COL == 255 || N_COL == 0) {
N_COL = 16;
}
if (N_LIN == 255 || N_LIN == 0) {
N_LIN = 2;
}
LCD_info();
// enable interrupts after start-up
GIE = 1;
// initialize vars
rcv = 1; // set ready to receive
bell_flag = 0;
bell_latch = 0;
bell_count = 0;
buf_sz = 0; // clear buffer size
buf_w_pos = 0; // clear buffer write cursor position
buf_r_pos = 0; // clear buffer read cursor position
LCD_CLS();
while(1) { // while forever...
if (buf_sz > 0 && !RCIF) {
cur_byte = buffer[buf_r_pos];
buf_r_pos++;
if (buf_r_pos > 63) buf_r_pos = 0;
buf_sz--;
if (cur_byte == CHR_BEL) { // handle bell char
bell_flag = 1;
} else if (cur_byte == CHR_DEL) { // backspace
if (POS_COL > 0) {
writeLCDcmd(CMD_LEFT);
writeLCDchar(' ');
writeLCDcmd(CMD_LEFT);
POS_COL--;
} else if (POS_LIN > 1) {
POS_LIN--;
writeLCDcmd(CMD_MOV + (LIN_ADR[POS_LIN - 1] + N_COL) - 1);
writeLCDchar(' ');
writeLCDcmd(CMD_LEFT);
POS_COL = N_COL - 1;
}
} else if (cur_byte == CHR_LF || cur_byte == CHR_CR) { // LF or CR
LCD_LF();
} else if (cur_byte == CHR_ESC) { // ESCAPE SEQUENCES
escaped = 1;
} else if (escaped) { // handle escape sequences
if (esc_seq == 0) { // not yet escaped - set ecsape sequence
if (cur_byte == 120) { // 'x' to change LCD configuration columns
esc_seq = 1;
esc_len = 0;
} else if (cur_byte == 121) { // 'y' to change LCD configuration lines
esc_seq = 2;
esc_len = 0;
} else if (cur_byte == 98) { // 'b' to fire bell output
bell_flag = 1;
escaped = 0;
} else if (cur_byte == 79) { // 'O' to latch bell output on
bell_latch = 1;
escaped = 0;
} else if (cur_byte == 111) { // 'o' to latch bell output off
BELL_PIN = 0;
bell_latch = 0;
bell_flag = 0;
escaped = 0;
} else if (cur_byte == 99) { // 'c' clear screen
LCD_CLS();
escaped = 0;
} else if (cur_byte == 72) { // 'H' home cursor
writeLCDcmd(CMD_HOME);
POS_COL = 0; // set column position
POS_LIN = 1; // set line position
escaped = 0;
} else if (cur_byte == 76) { // 'L' to turn backlight on
LED_PIN = 0;
escaped = 0;
} else if (cur_byte == 108) { // 'l' to turn backlight off
LED_PIN = 1;
escaped = 0;
} else { // not a valid escape sequence
escaped = 0;
}
} else if (esc_seq == 1 || esc_seq == 2) { // setting LCD columns or lines
if (esc_len <= 2 && cur_byte >= 48 && cur_byte <= 57) { // two numeric digits
esc_len++;
if (esc_len == 1) {
esc_val = (cur_byte - 48);
esc_val = esc_val * 10;
} else if (esc_len == 2) {
esc_val = esc_val + (cur_byte - 48);
if (esc_seq == 1) {
N_COL = esc_val;
writeEEPROMbyte(0, N_COL);
} else if (esc_seq == 2) {
N_LIN = esc_val;
writeEEPROMbyte(1, N_LIN);
}
escaped = 0;
esc_seq = 0;
esc_len = 0;
}
} else { // too many digits, clear out
escaped = 0;
esc_seq = 0;
esc_len = 0;
}
}
} else { // handle raw string data
POS_COL++; // incr cursor pos
// display boundary checking/handler
if (rcv && POS_COL > N_COL) {
LCD_LF();
}
writeLCDchar(cur_byte); // write char to display
}
}
if (bell_flag || bell_latch) {
if (bell_flag && bell_count < BELL_CYCLES) {
BELL_PIN = 1;
bell_count++;
} else if (bell_latch) {
BELL_PIN = 1;
} else {
BELL_PIN = 0;
bell_count = 0;
bell_flag = 0;
bell_latch = 0;
}
}
}//while
}//main |