;------------------------------------------------------------------------------------------------------------------------ ; Source code for the PIC16F873 based interfacing with HD44780 based 16x2 LCD. ;------------------------------------------------------------------------------------------------------------------------ ; ; **LCD Pinouts ; 1 Vss - Ground, 3rd pin of the potentiometer ; 2 Vcc - 5V DC, 1st pin of the potentiometer ; 3 Vee - Middle pin of the potentiometer ; 4 RS - RC0 (Data - 1, Instruction - 0) ; 5 R/W - RC1 (R - 1, W - 0) ; 6 E - RC2 (Enable Pulse) ; 7 DB0 - RB0 (LSB) ; 8 DB1 - RB1 ; 9 DB2 - RB2 ; 10 DB3 - RB3 (Lower 4 bits) ; 11 DB4 - RB4 (Upper 4 bits) ; 12 DB5 - RB5 ; 13 DB6 - RB6 ; 14 DB7 - RB7 (MSB) ; ; Instruction Cycle Time = 1 / (4MHz / 4) = 1us per instruction ;------------------------------------------------------------------------------------------------------------------------ LIST P=16F873 INCLUDE "p16f873.inc" ; ERRORLEVEL -302 __CONFIG _PWRTE_OFF & _HS_OSC & _WDT_OFF & _LVP_OFF & _BODEN_OFF; configuration switches N EQU 0x20 FIXDELAY EQU 0x21 ; General Purpose Registers. org 0x00 nop ; Reserved for ICD II. goto start start call initports ; Initialize Ports as output/inputs. call INITLCD ; Initialize LCD. main call testmsg ; Print test message on LCD forever goto $ ;------------------------------------------------------------------------------------------------------------------------ ; Subroutine to initialize the PORTs as Inputs or Outputs. ;------------------------------------------------------------------------------------------------------------------------ initports banksel PORTB clrf PORTB ; Clear PORTs. clrf PORTC banksel TRISB movlw 0x00 ; Define PORTB and PORTC as Outputs. movwf TRISB movwf TRISC return ;------------------------------------------------------------------------------------------------------------------------ ; Initialize the LCD. ;------------------------------------------------------------------------------------------------------------------------ INITLCD BANKSEL PORTB ; Select Bank for PORTB. MOVLW 0xE6 ; Call for 46ms delay CALL NDELAY ; Wait for VCC of the LCD to reach 5V BCF PORTC, 0 ; Clear RS to select Instruction Reg. BCF PORTC, 1 ; Clear R/W to write MOVLW B'00111011' ; Function Set to 8 bits, 2 lines and 5x7 dot matrix MOVWF PORTB CALL ENABLEPULSE CALL DELAY50 CALL ENABLEPULSE CALL DELAY50 CALL ENABLEPULSE CALL DELAY50 ; Call 50us delay and wait for instruction completion MOVLW B'00001000' ; Display OFF MOVWF PORTB CALL ENABLEPULSE CALL DELAY50 ; Call 50us delay and wait for instruction completion MOVLW B'00000001' ; Clear Display MOVWF PORTB CALL ENABLEPULSE MOVLW 0x09 ; Call 1.8ms delay and wait for instruction completion CALL NDELAY MOVLW B'00000010' ; Cursor Home MOVWF PORTB CALL ENABLEPULSE MOVLW 0x09 ; Call 1.8ms delay and wait for instruction completion CALL NDELAY MOVLW B'00001111' ; Display ON, Cursor ON, Blinking ON MOVWF PORTB CALL ENABLEPULSE CALL DELAY50 ; Call 50us delay and wait for instruction completion MOVLW B'00000110' ; Entry Mode Set, Increment & No display shift MOVWF PORTB CALL ENABLEPULSE CALL DELAY50 ; Call 50us delay and wait for instruction completion BSF PORTC, 0 ; Set RS to select Data Reg. BCF PORTC, 1 ; Clear R/W to write RETURN ;------------------------------------------------------------------------------------------------------------------------ ; Enable Pulse for writing or reading instructions or data ;------------------------------------------------------------------------------------------------------------------------ ENABLEPULSE BCF PORTC, 2 ; 2us LOW followed by 3us HIGH Enable Pulse and 2us LOW. NOP NOP BSF PORTC, 2 NOP NOP NOP BCF PORTC, 2 NOP NOP RETURN ;------------------------------------------------------------------------------------------------------------------------ ; N DELAY SUBROUTINE, delay in multiples of 200us up to 200us*255 = 51ms (or more) ;------------------------------------------------------------------------------------------------------------------------ NDELAY MOVWF N ; N is delay multiplier NOTOVER CALL DELAY200 ; Call for 200us DECFSZ N, 1 ; Decrease N by 1 GOTO NOTOVER ; The delay isn't done RETURN ;------------------------------------------------------------------------------------------------------------------------ ; FIXED 200us DELAY (Possibly more due to execution time of the DECFSZ instruction.) ;------------------------------------------------------------------------------------------------------------------------ DELAY200 MOVLW 0x42 ; 66 LOOPS MOVWF FIXDELAY ; 200us fixed delay NOTDONE200 DECFSZ FIXDELAY, 1 ; Decrement of FIXDELAY GOTO NOTDONE200 ; If 200us isn't up go back to NOTDONE200 RETURN ; If 200us is up then return to instruction. ;------------------------------------------------------------------------------------------------------------------------ ; FIXED 50us DELAY (Possibly more due to execution time of the DECFSZ instruction.) ;------------------------------------------------------------------------------------------------------------------------ DELAY50 MOVLW 0x10 ; 16 LOOPS MOVWF FIXDELAY ; 50us fixed delay NOTDONE50 DECFSZ FIXDELAY, 1 ; Decrement of FIXDELAY GOTO NOTDONE50 ; If 50us isn't up go back to NOTDONE50 RETURN ; If 50us is up then return to instruction. ;------------------------------------------------------------------------------------------------------------------------ ; FIXED 20us DELAY (Possibly more due to execution time of the DECFSZ instruction.) ;------------------------------------------------------------------------------------------------------------------------ DELAY20 MOVLW 0x7 ; 7 LOOPS MOVWF FIXDELAY ; 50us fixed delay NOTDONE20 DECFSZ FIXDELAY, 1 ; Decrement of FIXDELAY GOTO NOTDONE20 ; If 50us isn't up go back to NOTDONE50 RETURN ; If 50us is up then return to instruction. ;------------------------------------------------------------------------------------------------------------------------ ; Fast Directive to write characters to LCD. ;------------------------------------------------------------------------------------------------------------------------ PUTCHAR MOVWF PORTB ; A quicker way of writing characters to LCD. CALL ENABLEPULSE CALL CHKBUSY RETURN ;------------------------------------------------------------------------------------------------------------------------ ; Subroutine to check for the BUSY flag. Mostly used for instructions that follows up a character write. ;------------------------------------------------------------------------------------------------------------------------ CHKBUSY bcf PORTC, 0 ; Clear RS to select Instruction Reg. bsf PORTC, 1 ; Set R/W to read. banksel TRISB ; Select Bank for TRISC. movlw 0xFF ; Define all PORTC Pins as Inputs. movwf TRISB banksel PORTC ; Select Bank for PORTC. bsf PORTC, 2 ; I tried to write my own code for this part initially but I wasn't successful. movf PORTB, w ; Therefore, I implemented a portion of Peter Ouwehand's LCD Code. bcf PORTC, 2 ; Will look more into the BUSY flag of the LCD. andlw 0x80 ; Credits to Peter Ouwehand for his code here. :) btfss STATUS, Z goto CHKBUSY banksel TRISB ; Select Bank for TRISB. movlw 0x00 ; Define all PORTC Pins as Outputs. movwf TRISB banksel PORTC ; Select Bank for PORTA, B, and C. bsf PORTC, 0 ; Set RS to select Data Register. bcf PORTC, 1 ; Clear R/W to write. return ;------------------------------------------------------------------------------------------------------------------------ ; Position Cursor to the next line. ;------------------------------------------------------------------------------------------------------------------------ nextline banksel PORTC bcf PORTC, 0 ; Select Instructions Register. bcf PORTC, 1 ; Select Write. movlw b'11000000' ; Shift cursor to second line at 0x40 RAM address on LCD. call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; Clear screen and Cursor home. ;------------------------------------------------------------------------------------------------------------------------ clrscreen banksel PORTC bcf PORTC, 0 ; Clear RS to select Instructions Register. bcf PORTC, 1 ; Clear R/W to select Write. banksel PORTB MOVLW B'00000001' ; Clear Display call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; Position Cursor to home position. ;------------------------------------------------------------------------------------------------------------------------ cursorhome banksel PORTC bcf PORTC, 0 ; Select Instructions Register. bcf PORTC, 1 ; Select Write. movlw b'00000010' ; Position cursor to home position. call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; A test message. ;------------------------------------------------------------------------------------------------------------------------ testmsg movlw A'I' ; Displays "I m working fine" call PUTCHAR ; "Line 2 is alrite" movlw A' ' call PUTCHAR movlw A'm' call PUTCHAR movlw A' ' call PUTCHAR movlw A'w' call PUTCHAR movlw A'o' call PUTCHAR movlw A'r' call PUTCHAR movlw A'k' call PUTCHAR movlw A'i' call PUTCHAR movlw A'n' call PUTCHAR movlw A'g' call PUTCHAR movlw A' ' call PUTCHAR movlw A'f' call PUTCHAR movlw A'i' call PUTCHAR movlw A'n' call PUTCHAR movlw A'e' call PUTCHAR call nextline movlw A'L' call PUTCHAR movlw A'i' call PUTCHAR movlw A'n' call PUTCHAR movlw A'e' call PUTCHAR movlw A' ' call PUTCHAR movlw A'2' call PUTCHAR movlw A' ' call PUTCHAR movlw A'i' call PUTCHAR movlw A's' call PUTCHAR movlw A' ' call PUTCHAR movlw A'a' call PUTCHAR movlw A'l' call PUTCHAR movlw A'r' call PUTCHAR movlw A'i' call PUTCHAR movlw A't' call PUTCHAR movlw A'e' call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; End of programme. ;------------------------------------------------------------------------------------------------------------------------ end