;------------------------------------------------------------------------------------------------------------------------ ; Source code for the PIC16F873 based interfacing of LCD with a 4x4 matrix keypad featuring the MM74C922 Keypad Encoder. ;------------------------------------------------------------------------------------------------------------------------ ; ; **Keypad Inputs from the MM74C922 ; Data A - RA0 (LSB) ; Data B - RA1 ; Data C - RA2 ; Data D - RA3 (MSB) ; Data Available - RA5 (Goes High when a key is hit.) ; ; **Encoded Keypad Codes Input to PORTA. ; 0000 - 1 0100 - 4 1000 - 7 1100 - * ; 0001 - 2 0101 - 5 1001 - 8 1101 - 0 ; 0010 - 3 0110 - 6 1010 - 9 1110 - # ; 0011 - A 0111 - B 1011 - C 1111 - D ; ; **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 - RB0 (Data - 1, Instruction - 0) ; 5 R/W - RB1 (R - 1, W - 0) ; 6 E - RB2 (Enable Pulse) ; 7 DB0 - RC0 (LSB) ; 8 DB1 - RC1 ; 9 DB2 - RC2 ; 10 DB3 - RC3 (Lower 4 bits) ; 11 DB4 - RC4 (Upper 4 bits) ; 12 DB5 - RC5 ; 13 DB6 - RC6 ; 14 DB7 - RC7 (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 charhold EQU 0x2B ; General Purpose Registers. linepointer EQU 0x2C spacecounter EQU 0x2D N EQU 0x2E FIXDELAY EQU 0x2F org 0x00 nop ; Reserved for ICD II. goto start start call initports ; Initialize the PORTs. call INITLCD ; Initialize the LCD. movlw d'16' ; Define spacecounter as 16. movwf spacecounter clrf charhold ; Clear registers. clrf linepointer main btfss PORTA, 5 ; Wait for Keypad Inputs. goto main call decodedata ; When key is hit, decode the input data. call displaykey ; Display the key that is hit. goto main ;------------------------------------------------------------------------------------------------------------------------ ; Subroutine to initialize the PORTs as Inputs or Outputs. ;------------------------------------------------------------------------------------------------------------------------ initports clrf PORTA ; Clear the PORTs. clrf PORTB clrf PORTC banksel TRISA ; Select TRISA, B, and C banks. movlw b'00111111' ; Define PORTA as Inputs. movwf TRISA banksel ADCON1 ; Select Bank for ADCON1. movlw b'00000110' ; Define all PORTA pins as Digital. movwf ADCON1 movlw 0x00 ; Define PORTB and PORT C 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 PORTB, 0 ; Clear RS to select Instruction Reg. BCF PORTB, 1 ; Clear R/W to write MOVLW B'00111011' ; Function Set to 8 bits, 2 lines and 5x7 dot matrix MOVWF PORTC 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 PORTC CALL ENABLEPULSE CALL DELAY50 ; Call 50us delay and wait for instruction completion MOVLW B'00000001' ; Clear Display MOVWF PORTC CALL ENABLEPULSE MOVLW 0x09 ; Call 1.8ms delay and wait for instruction completion CALL NDELAY MOVLW B'00000010' ; Cursor Home MOVWF PORTC 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 PORTC CALL ENABLEPULSE CALL DELAY50 ; Call 50us delay and wait for instruction completion MOVLW B'00000110' ; Entry Mode Set, Increment & No display shift MOVWF PORTC CALL ENABLEPULSE CALL DELAY50 ; Call 50us delay and wait for instruction completion BSF PORTB, 0 ; Set RS to select Data Reg. BCF PORTB, 1 ; Clear R/W to write RETURN ;------------------------------------------------------------------------------------------------------------------------ ; Enable Pulse for writing or reading instructions or data ;------------------------------------------------------------------------------------------------------------------------ ENABLEPULSE BCF PORTB, 2 ; 2us LOW followed by 3us HIGH Enable Pulse and 2us LOW. NOP NOP BSF PORTB, 2 NOP NOP NOP BCF PORTB, 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 PORTC ; 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 PORTB, 0 ; Clear RS to select Instruction Reg. bsf PORTB, 1 ; Set R/W to read. banksel TRISC ; Select Bank for TRISC. movlw 0xFF ; Define all PORTC Pins as Inputs. movwf TRISC banksel PORTC ; Select Bank for PORTC. bsf PORTB, 2 ; I tried to write my own code for this part initially but I wasn't successful. movf PORTC, w ; Therefore, I implemented a portion of Peter Ouwehand's LCD Code. bcf PORTB, 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 TRISC ; Select Bank for TRISC. movlw 0x00 ; Define all PORTC Pins as Outputs. movwf TRISC banksel PORTB ; Select Bank for PORTA, B, and C. bsf PORTB, 0 ; Set RS to select Data Register. bcf PORTB, 1 ; Clear R/W to write. return ;------------------------------------------------------------------------------------------------------------------------ ; Subroutine to decode the Keypad data input in PORTA. ;------------------------------------------------------------------------------------------------------------------------ decodedata call DELAY20 ; Wait for some key debouncing to settle down. movf PORTA, w ; Move input data from PORTA to WREG. andlw 0x0F ; Strip the upper 4 bits. key1 sublw d'0' ; The codes below simply compares the encoded data from the 74C922 to each of the possible btfss STATUS, Z ; key output. Whenever a match is found, it will output the corresponding character in goto key2 ; ASCII to be displayed at the LCD. movlw A'1' goto decodedone key2 movf PORTA, w sublw d'1' btfss STATUS, Z goto key3 movlw A'2' goto decodedone key3 movf PORTA, w sublw d'2' btfss STATUS, Z goto key4 movlw A'3' goto decodedone key4 movf PORTA, w sublw d'3' btfss STATUS, Z goto key5 movlw A'A' goto decodedone key5 movf PORTA, w sublw d'4' btfss STATUS, Z goto key6 movlw A'4' goto decodedone key6 movf PORTA, w sublw d'5' btfss STATUS, Z goto key7 movlw A'5' goto decodedone key7 movf PORTA, w sublw d'6' btfss STATUS, Z goto key8 movlw A'6' goto decodedone key8 movf PORTA, w sublw d'7' btfss STATUS, Z goto key9 movlw A'B' goto decodedone key9 movf PORTA, w sublw d'8' btfss STATUS, Z goto key10 movlw A'7' goto decodedone key10 movf PORTA, w sublw d'9' btfss STATUS, Z goto key11 movlw A'8' goto decodedone key11 movf PORTA, w sublw d'10' btfss STATUS, Z goto key12 movlw A'9' goto decodedone key12 movf PORTA, w sublw d'11' btfss STATUS, Z goto key13 movlw A'C' goto decodedone key13 movf PORTA, w sublw d'12' btfss STATUS, Z goto key14 movlw A'*' goto decodedone key14 movf PORTA, w sublw d'13' btfss STATUS, Z goto key15 movlw A'0' goto decodedone key15 movf PORTA, w sublw d'14' btfss STATUS, Z goto key16 movlw A'#' goto decodedone key16 movf PORTA, w sublw d'15' btfss STATUS, Z goto key1 movlw A'D' goto decodedone decodedone movwf charhold ; Pass ASCII character to charhold. return ;------------------------------------------------------------------------------------------------------------------------ ; Displays the character on the LCD and corrects the display accordingly. ;------------------------------------------------------------------------------------------------------------------------ displaykey decfsz spacecounter, f ; Decrease the spacecounter by 1. goto notendline ; If it ain't 0, goto notendline to display the character. btfsc linepointer, 0 ; Check if End of Line 1 or 2. goto endofline2 ; If bit 0 is Set, therefore end of line 2. goto endofline1 ; If bit 0 is Clr, therefore end of line 1. endofline1 call nextline ; Position Cursor to the Next Line. goto notendline endofline2 call clrscreen ; Clear screen and return cursor to home. goto notendline notendline movf charhold, w ; Pass the ASCII from charhold back to PORTC in PUTCHAR. call PUTCHAR ; Display on LCD. call DELAY20 ; Wait for debouncing to settle. waitrelease btfsc PORTA, 5 ; Wait for the key to be released. goto waitrelease call DELAY20 ; Wait for debouncing to settle again. return ;------------------------------------------------------------------------------------------------------------------------ ; Position Cursor to the next line. ;------------------------------------------------------------------------------------------------------------------------ nextline banksel PORTB bcf PORTB, 0 ; Select Instructions Register. bcf PORTB, 1 ; Select Write. movlw b'11000000' ; Shift cursor to second line at 0x40 RAM address on LCD. call PUTCHAR movlw d'16' ; Restore spacecounter. movwf spacecounter bsf linepointer, 0 ; Set bit 0 of linepointer to indicate Line 2 of LCD. return ;------------------------------------------------------------------------------------------------------------------------ ; Clear screen and Cursor home. ;------------------------------------------------------------------------------------------------------------------------ clrscreen banksel PORTB bcf PORTB, 0 ; Clear RS to select Instructions Register. bcf PORTB, 1 ; Clear R/W to select Write. banksel PORTC MOVLW B'00000001' ; Clear Display call PUTCHAR movlw d'16' ; Restore spacecounter. movwf spacecounter bcf linepointer, 0 ; Clear bit 0 of linepointer to indicate Line 1 of LCD. return end