PIC16F88 0D Multiplex |
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PORTA selects one of the four displays by setting the appropriate pin high.
PORTB lights the wanted segments on the selected display by setting the appropriate pin/s low.
If all four segments are used, they are each active 25% of the time. This makes the display dimmer than it might otherwise be.
To cure this disadvantage, the data would need to be latched for each display, adding complexity to the circuit.
The current could be quadrupled but not without blowing the microcontroller. High current drivers could be added though.
This program activates each display for about 0. 25 ms every 1 ms. This is a frame rate of 1000 Hz.
Flicker becomes noticeable below 50 Hz and intrusive below 25 Hz.
It's often useful to have a quick and dirty program to test the hardware. This one activates each segment in turn slowly enough to see if each one lights up.
;*******************************************************************************
; INPUT: None.
; PROCESS: One by one, activate each of the 32 display segments.
; Repeat the test for ever.
; OUTPUT: One LED at a time will light up. Every LED should flash once.
;*******************************************************************************
; PIC16F88 Configuration Bit Settings
;*******************************************************************************
#include "p16f88.inc"
; CONFIG1 and CONFIG2
__CONFIG _CONFIG1, _FOSC_INTOSCIO & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF & _BOREN_ON & _LVP_OFF & _CPD_OFF & _WRT_OFF & _CCPMX_RB0 & _CP_OFF
__CONFIG _CONFIG2, _FCMEN_ON & _IESO_ON
;*******************************************************************************
; Uninitialised Data - Reserve bytes here ...
;*******************************************************************************
UDATA
DelCount RES 1 ; reserves 1 byte - OK with simulator run-time watch
RES_VECT CODE 0x0000 ; processor reset to vector address zero
GOTO START ; go to beginning of program
MAIN_PROG CODE ; let linker place main program
START: ; INITIALISATION
bsf STATUS, RP0 ; Select bank 1.
movlw b'00000000' ; Set all port pins to output / Disable ADC / Set for digital i/o
movwf ADCON1 ; Disble ADC module (Never leave this to chance)
movwf ANSEL ; Set analog i/o for digital i/o (Never leave this to chance)
movwf TRISA ; Set porta - RA5 is input only so this bit is ignored
movwf TRISB ; Set portb
bcf STATUS, RP0 ; Select bank 0.
MYREPEAT:
MOVLW 0x2 ; Left hand segments
MOVWF PORTA ; Multiplex port output
CALL test_display
MOVLW 0x4 ; Second segments
MOVWF PORTA ; Multiplex port output
CALL test_display
MOVLW 0x8 ; Third segments
MOVWF PORTA ; Multiplex port output
CALL test_display
MOVLW 0x10 ; Right hand segments
MOVWF PORTA ; Multiplex port output
CALL test_display
GOTO MYREPEAT
;*******************************************************************************
; Test Segments
;*******************************************************************************
test_display:
MOVLW 0xFE ; Segment A
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0xFD ; Segment B
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0xFB ; Segment C
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0xF7 ; Segment D
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0xEF ; Segment E
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0xDF ; Segment F
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0xBF ; Segment G
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0x7F ; Segment Decimal Point
MOVWF PORTB ; Multiplex port output
CALL MyDelay
MOVLW 0xFF ; Blank Display
MOVWF PORTB ; Multiplex port output
CALL MyDelay
RETURN
;*******************************************************************************
; Count down from 255 to zero and execute some NOPs to slow everything down.
;*******************************************************************************
MyDelay:
MOVLW 0xFF
MOVWF DelCount
MyDeloop:
NOP
NOP
NOP
NOP
DECFSZ DelCount, F
GOTO MyDeloop
RETURN
END
;*******************************************************************************
; PIC16F88 Configuration Bit Settings
;*******************************************************************************
#include "p16F88.inc"
; CONFIG1 - Internal oscillator - Want I/O - Everything else turned off
__CONFIG _CONFIG1, _FOSC_INTOSCIO & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF & _BOREN_OFF & _LVP_OFF & _CPD_OFF & _WRT_OFF & _CCPMX_RB0 & _CP_OFF
; CONFIG2 - Turn on both
__CONFIG _CONFIG2, _FCMEN_ON & _IESO_ON
;*******************************************************************************
; Uninitialised Data - Reserve bytes here ...
;*******************************************************************************
UDATA
ones RES 1 ; reserves 1 byte - OK with simulator run-time watch
tens RES 1
hundreds RES 1
thousands RES 1
DelCount RES 1
PortaTemp RES 1 ; To save and restore PORTA during the interrupt
;*******************************************************************************
; 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 CLOCK_INIT ; Set the clock frequency
CALL PORT_INIT ; Set up I/O Port Directions
CALL VAR_INIT ; Initialise Variable/s
CALL TIMER_INIT ; Set up Timer0
CALL TIMER_START ; Start Timer0
BANKSEL PORTA ; Clear RP0 in STATUS to select Memory Bank 0
GOTO MUX_Loop ; Jump to Infinite Loop to Multiplex the Displays
;*******************************************************************************
; INTERRUPT SUBROUTINE
; This ought to save and restore the complete context
; In this example PORTA must be saved and restored
;*******************************************************************************
ISR_HANDLER:
MOVWF PortaTemp ; Save PORTA - Prevent display glitches
CALL IncCounter ; Add one to the four digit counter
CALL TIMER_START ; Start Timer0
MOVF PortaTemp, W ; Restore PORTA - Prevent display glitches
RETFIE ; Return from interrupt
;*******************************************************************************
; INITIALISE CLOCK FREQUENCY - 4MHz - 1 microsecond per instruction
;*******************************************************************************
CLOCK_INIT:
BANKSEL OSCCON
movlw b'01100000' ; -110---- 4 MHz
movwf OSCCON ; At 4 MHz it's one microsecond per line of code.
RETURN
;*******************************************************************************
; INITIALISE PORTS
;*******************************************************************************
PORT_INIT:
BANKSEL TRISA ; Set RP0 in STATUS to select Memory Bank 1
MOVLW b'00000000' ; Disable ADC / Set for digital i/o
MOVWF ADCON1 ; Disble ADC module (Never leave this to chance)
MOVWF ANSEL ; Turn off analog i/o. Select digital i/o (Never leave this to chance)
MOVLW b'00000000' ; Eight output lines
MOVWF TRISA ; Set PORTA as Outputs - Remember RA5 is input only
MOVWF TRISB ; Set PORTB as Outputs
RETURN
;*******************************************************************************
; INITIALISE VARIABLES
;*******************************************************************************
VAR_INIT:
BANKSEL PORTA ; Clear RP0 in STATUS to select Memory Bank 0
MOVLW d'0'. ; Initial value
MOVWF ones ; initialise to zero
MOVLW d'0' ; Just in case we don't want another zero
MOVWF tens ; initialise to zero
MOVLW d'0'
MOVWF hundreds ; initialise to zero
MOVLW d'0'
MOVWF thousands ; initialise to zero
RETURN
;*******************************************************************************
; INITIALISE TIMER0
;*******************************************************************************
TIMER_INIT:
BANKSEL TRISA ; Set RP0 in STATUS to select Memory Bank 1
CLRWDT ; Clear the Watchdog Timer and prescaler
MOVLW b'00000110' ; 1:64 TMR0 rate prescaling - If simulating reduce to 1:4 or 1:8
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:
BANKSEL PORTA ; Clear RP0 in STATUS to select Memory Bank 0
BCF INTCON, TMR0IF ; Clear the TMR0IF flag
MOVLW d'10' ; TMR0 counts from 10 to 256 - If simulating, 250 might be better
MOVWF TMR0 ; 10 copied into TMR0
RETURN
;*******************************************************************************
; MUX_Loop sends the multiplexed binary to the four displays
; At regular intervals, it's interrupted and one is added to the counter
;*******************************************************************************
MUX_Loop:
MOVLW 0x0 ; Blank digit - prevent display glitches
MOVWF PORTA
MOVF ones, W ; Copy the ones digit into WREG
CALL SEV_SEG ; Return the binary to light the segments into WREG
MOVWF PORTB
MOVLW 0x10 ; Show right hand digit by
MOVWF PORTA ; copying 0x10 to PORTA
MOVLW 0x30
MOVWF DelCount
Deloop1:
NOP
NOP
DECFSZ DelCount, F
GOTO Deloop1
MOVLW 0x0 ; Blank second digit - prevent display glitches
MOVWF PORTA
MOVF tens, W ; Copy the tens digit into WREG
CALL SEV_SEG ; Return the binary to light the segments into WREG
MOVWF PORTB
MOVLW 0x8 ; Show second digit by
MOVWF PORTA ; copying 0x8 to PORTA
MOVLW 0x30
MOVWF DelCount
Deloop2:
NOP
NOP
DECFSZ DelCount, F
GOTO Deloop2
MOVLW 0x0 ; Blank third digit - prevent display glitches
MOVWF PORTA
MOVF hundreds, W ; Copy the hundreds digit into WREG
CALL SEV_SEG ; Return the binary to light the segments into WREG
MOVWF PORTB
MOVLW 0x4 ; Show third digit by
MOVWF PORTA ; copying 0x4 to PORTA
MOVLW 0x30
MOVWF DelCount
Deloop3:
NOP
NOP
DECFSZ DelCount, F
GOTO Deloop3
MOVLW 0x0 ; Blank left digit - prevent display glitches
MOVWF PORTA
MOVF thousands, W ; Copy the thousands digit into WREG
CALL SEV_SEG ; Return the binary to light the segments into WREG
MOVWF PORTB
MOVLW 0x2 ; Show left hand digit by
MOVWF PORTA ; copying 0x2 to PORTA
MOVLW 0x30
MOVWF DelCount
Deloop4:
NOP
NOP
DECFSZ DelCount, F
GOTO Deloop4
GOTO MUX_Loop
;*******************************************************************************
; Add one to the four digit counter. If it was on 9999 reset it to zero
;*******************************************************************************
IncCounter:
Ones:
INCF ones
MOVLW d'10'
SUBWF ones, W
BTFSS STATUS, Z ; Will be set if ones has reached 10
RETURN ; No need to do the rest
Tens:
MOVLW 0x00
MOVWF ones ; Reset ones to zero
INCF tens
MOVLW d'10'
SUBWF tens, W
BTFSS STATUS, Z ; Will be set if tens has reached 100
RETURN ; No need to do the rest
Hundreds:
MOVLW 0x00
MOVWF tens ; Reset tens to zero
INCF hundreds
MOVLW d'10'
SUBWF hundreds, W
BTFSS STATUS, Z ; Will be set if hundreds has reached 1000
RETURN ; No need to do the rest
Thousands:
MOVLW 0x00
MOVWF hundreds ; Reset hundreds to zero
INCF thousands
MOVLW d'10'
SUBWF thousands, W
BTFSS STATUS, Z ; Will be set if thousands has reached 10000
RETURN ; No need to do the rest
MOVLW 0x00
MOVWF thousands ; Reset thousands to zero
RETURN
;*******************************************************************************
; DATA TABLE FOR THE SEVEN SEGMENT DISPLAY
; INPUT: The table position in WREG
; PROCESS: Add WREG to PCL. It's like "GOTO Table Position"
; OUTPUT: Return the data using RETLW
;*******************************************************************************
SEV_SEG:
addwf PCL, 1 ; GOTO table position and Return the byte in the WREG
retlw 0xC0 ; 0 - Turn on the correct segments to show a zero
retlw 0xF9 ; 1
retlw 0xA4 ; 2
retlw 0xB0 ; 3
retlw 0x99 ; 4
retlw 0x92 ; 5
retlw 0x82 ; 6
retlw 0xF8 ; 7
retlw 0x80 ; 8
retlw 0x98 ; 9
retlw 0x7F ; Decimal Point
END
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