PIC16F88 0B Digital I/O |
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The program polls PORTA and copies the input data to PORTB.
All the output LEDs are off untill a push button is pressed.
The polling is triggered by a Timer0 interrupt.
It's interesting to run this code with the switch board unplugged.
The floating inputs pick up random data from the electrical noise in the environment so the output LEDs flash unpredictably.
Never leave floating inputs!
;******************************************************************************* ; PIC16F88 Configuration Bit Settings ;******************************************************************************* #include "p16F88.inc" ; CONFIG1 __CONFIG _CONFIG1, _FOSC_INTOSCIO & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF & _BOREN_OFF & _LVP_OFF & _CPD_OFF & _WRT_OFF & _CCPMX_RB0 & _CP_OFF ; CONFIG2 __CONFIG _CONFIG2, _FCMEN_ON & _IESO_ON ;******************************************************************************* ; Uninitialised Data - Reserve bytes here ... ;******************************************************************************* UDATA PortByte RES 1 ; reserves 1 byte - OK with simulator debug ;******************************************************************************* ; RESET VECTOR ;******************************************************************************* RES_VECT CODE 0x0000 ; processor reset vector GOTO CODE_INIT ; beginning of program, initialise stuff ;******************************************************************************* ; INTERRUPT HANDLING ;******************************************************************************* ISR CODE 0x0004 ; The interrupt vector location is always 0x0004 GOTO ISR_HANDLER ; Jump to the Interrupt handling code ;******************************************************************************* ; MAIN PROGRAM - CODE INITIALISATION ;******************************************************************************* MAIN_PROG CODE ; let linker place main program CODE_INIT: ; INITIALISATION CALL PORT_INIT ; Set up I/O Port Directions CALL TIMER_INIT ; Set up Timer0 CALL TIMER_START ; Start Timer0 GOTO IDLE_LOOP ; Jump to the Infinite Idle Loop ;******************************************************************************* ; INTERRUPT SUBROUTINE ; This ought to save and restore the context ; It's not secessary in this simple example ;******************************************************************************* ISR_HANDLER: BCF STATUS, RP0 ; Select memory bank 0. MOVF PORTA, 0 ; Copy PORTA to WREG MOVWF PortByte CALL SET_PORTB CALL TIMER_START ; Re-Start Timer0 RETFIE ; Return from interrupt ;******************************************************************************* ; INITIALISE PORTS ;******************************************************************************* PORT_INIT: ; Use PIC16F88 Data Sheet method BANKSEL PORTA ; select bank of PORTA (Bank 1) CLRF PORTA ; Initialize PORTA by ; clearing output ; data latches BANKSEL ANSEL ; Select Bank of ANSEL MOVLW 0x00 ; Configure all pins MOVWF ANSEL ; as digital inputs MOVLW 0xFF ; Value used to initialize data direction (8 Inputs) MOVWF TRISA ; Set RA<7:0> as inputs MOVLW 0x00 ; Value used to initialize data direction (8 Outputs) MOVWF TRISB ; Set RA<7:0> as out6puts RETURN ;******************************************************************************* ; INITIALISE TIMER0 ;******************************************************************************* TIMER_INIT: BSF STATUS, RP0 ; Select memory bank 1. CLRWDT ; Clear the Watchdog Timer and prescaler MOVLW b'00000010' ; 1:8 Prescaling MOVWF OPTION_REG ; The prescaler settings are stored in OPTION_REG BSF INTCON, GIE ; Turn on interupts globally BSF INTCON, TMR0IE ; Turn on Timer0 interupts RETURN ;******************************************************************************* ; START TIMER ;******************************************************************************* TIMER_START: BCF STATUS, RP0 ; Select memory bank 0. BCF INTCON, TMR0IF ; Clear the TMR0IF flag MOVLW d'250' ; TMR0 counts from 250 to 256 MOVWF TMR0 ; 250 copied into TMR0 RETURN ;******************************************************************************* ; Send data to the ports ;******************************************************************************* SET_PORTB: BCF STATUS, RP0 ; Select memory bank 0. MOVF PortByte, 0 ; Copy MyCount to WREG MOVWF PORTB ; Copy WREG to PORTB RETURN ;******************************************************************************* ; The Idle Loop ; MS Windows has an "idle process" which waits for the user to do something. ;******************************************************************************* IDLE_LOOP: NOP NOP ; NOPs make the code execution obvious in the simulator NOP ; Leave them out in real life NOP GOTO IDLE_LOOP END
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