TITLE "Digital voltmeter" LIST P=PIC12F508, R=DEC INCLUDE "p12f508.inc" __CONFIG _CP_OFF & _MCLRE_OFF & _WDT_OFF & _IntRC_OSC #define ENA GPIO,0 ; MAX7221 interface: CS #define SDT GPIO,1 ; data in #define SCK GPIO,2 ; clock #define SCL 5 ; I2C clock pin setup #define SDA 4 ; I2C data pin setup #define SDA_in b'011000' ; I2C data line setup for input #define SDA_out b'001000' ; I2C data line setup for output #define DP 0 ; decimal point bit #define ch2 5 ; MCP3422 channel selection bit CBLOCK 0x07 ; data segment del, cnt, tmp:2 ; temporary variables n:2, nn:2 ; storage for ADC output of MCP3422 dat:2, dataIO ; data interface for MAX7221 and MCP3422 ACK, channel thousands1, hundreds1, tens1, units1 ; storage for BCD of positive supply thousands2, hundreds2, tens2, units2 ; storage for BCD of negative supply ENDC ORG 0 ; code segment clrf GPIO ; initialize the I/O port bsf ENA ; disable writing to MAX7221 bsf GPIO, SCL ; set I2C clock line high movlw SDA_in ; enable input on SDA pin tris GPIO ; save changes in TRISIO movlw b'11011111' ; enable GPIO:2 for output option ; TMR0 will be then clocked by FOSC call init_MAX7221 ; initialize the LED driver goto loop ; proceed with the main program loop ;//////////////// procedures delay ; delay for the number of msec in del movlw 200 ; set up delay counter movwf cnt goto $+1 ; this inner loop takes 1us*5*200 = 1ms decfsz cnt, f ; for PIC @ 4 MHz goto $-2 decfsz del, f ; the outer loop counter goto delay retlw 0 encode7seg ; bdafgcep andlw 0x0F ; make sure that W < 16 addwf PCL, f retlw b'11110110' ; code for 0 retlw b'10000100' ; code for 1 retlw b'11101010' ; code for 2 retlw b'11101100' ; code for 3 retlw b'10011100' ; code for 4 retlw b'01111100' ; code for 5 retlw b'01111110' ; code for 6 retlw b'10100100' ; code for 7 retlw b'11111110' ; code for 8 retlw b'11111100' ; code for 9 retlw b'00001000' ; code for - retlw b'01011110' ; code for b retlw b'01110010' ; code for C retlw b'11001110' ; code for d retlw b'01111010' ; code for E retlw b'00111010' ; code for F ;;;;;;;;;;;;;;;;;;;;;;;;;;; interface with MAX7221 init_MAX7221 clrf tmp incf tmp, f ; digits clear loop movf tmp, w movwf dat+1 ; digit address clrf dat call write_MAX7221 btfss tmp, 3 goto $-6 movlw 0x09 movwf dat+1 ; decode register clrf dat ; disable decoding for all digits call write_MAX7221 movlw 0x0A movwf dat+1 ; intensity register movlw 15 movwf dat ; set max intensity 15/16 call write_MAX7221 movlw 0x0B movwf dat+1 ; scan limit register movlw 7 movwf dat ; scan 8 digits call write_MAX7221 movlw 0x0C movwf dat+1 ; config register movlw 1 ; normal operation movwf dat call write_MAX7221 movlw 0x0F movwf dat+1 ; display test register clrf dat ; normal operation call write_MAX7221 retlw 0 write_MAX7221 ; write a 16-bit word; first byte is reg address movlw 16 ; bits counter movwf cnt bcf SCK ; make sure that SCK=0 bcf ENA ; enable the device write_loop rlf dat, f rlf dat+1, f ; shift out MSB to btfsc STATUS, C bsf SDT btfss STATUS, C bcf SDT ; the data line is set up now bsf SCK ; clock up nop ; short delay bcf SCK ; ... and down decfsz cnt, f ; all bits sent? goto write_loop ; not yet bsf ENA ; yes - latch in the data and exit retlw 0 ;;;;;;;;;;;;;;;;;;;;;;; interface with MCP3422 requestData call start_I2C ; start communication movlw b'11010000' ; MCP3422 address and write movwf dataIO call write_I2C ; write adress byte movlw b'10000100' ; single conversion request addwf channel, w ; select channel movwf dataIO ; 14-bit, PGA=1 call write_I2C ; write configuration byte call stop_I2C ; terminate communication retlw 0 getData call start_I2C ; start communication movlw b'11010001' ; MCP3422 address and read movwf dataIO call write_I2C clrf ACK ; setup for ACK signal call read_I2C ; get MSB movf dataIO, w btfss channel, ch2 movwf nn+1 ; save it in nn+1 btfsc channel, ch2 movwf n+1 incf ACK, f ; setup for NACK signal call read_I2C ; get MSB movf dataIO, w btfss channel, ch2 movwf nn ; save it in nn btfsc channel, ch2 movwf n call stop_I2C ; terminate communication retlw 0 ;;;;;;;;;;;;;;;;;;;;;;; implementation of the I2C interface ; ___ ; DATA: |_______ ; ______ ; SCK : |___ start_I2C ; start setup for I2C interface movlw SDA_in tris GPIO ; pull high SDA bsf GPIO, SCL ; pull high SCL nop ; delay slot bcf GPIO, SDA movlw SDA_out tris GPIO ; set data low goto $+1 ; wait for slave to detect it bcf GPIO, SCL ; set clock low retlw 0 ; ___ ; DATA: ______| ; ______ ; SCK : ___| stop_I2C ; stop setup for I2C interface bcf GPIO, SCL ; make sure that clock and data bcf GPIO, SDA movlw SDA_out tris GPIO ; are low goto $+1 bsf GPIO, SCL ; release clock line nop movlw SDA_in tris GPIO ; release data line retlw 0 write_I2C ; write a byte to the I2C bus bcf GPIO, SCL ; make sure that clock is low movlw SDA_out tris GPIO ; configure SDA line for output movlw 8 movwf cnt ; bits counter w_loop bcf GPIO, SDA ; preset 0 on data line rlf dataIO, f ; get the rightmost data bit btfsc STATUS, C movlw SDA_in ; preset data line high (data=1) btfss STATUS, C movlw SDA_out ; preset data line low (data=0) tris GPIO ; configure the data pin bsf GPIO, SCL ; raise clock up nop bcf GPIO, SCL ; ... and down decfsz cnt, f goto w_loop ; repeat this 8 times movlw SDA_in ; release the data line tris GPIO ; get ACK from slave goto $+1 ; let slave respond bsf GPIO, SCL ; clock up nop ; slave responds OK (hopefully) bcf GPIO, SCL ; clock down retlw 0 read_I2C ; read byte from I2C bus bcf GPIO, SCL ; make sure that clock is low movlw 8 ; we assume that data line is released movwf cnt ; bits counter r_loop bsf GPIO, SCL ; clock up bcf STATUS, C btfsc GPIO, SDA ; read data pin bsf STATUS, C ; C = data bit bcf GPIO, SCL ; clock down rlf dataIO, f ; insert it into the data byte decfsz cnt, f goto r_loop ; repeat this 8 times movf ACK, f ; set Z flag bcf GPIO, SDA movlw SDA_in btfsc STATUS, Z movlw SDA_out ; ACK signal tris GPIO bsf GPIO, SCL ; clock up goto $+1 goto $+1 nop bcf GPIO, SCL ; clock down movlw SDA_in tris GPIO ; release the data line retlw 0 ;//////////////// MAIN LOOP loop movlw 200 movwf del call delay ; 0.2 sec delay clrf channel call requestData ; request data from channel 1 movlw 25 movwf del call delay ; 25 msec ADC delay call getData ; get ADC code for negative voltages btfss nn+1, 7 ; ADC code must not be negative goto $+3 clrf nn ; clear nn (2 bytes) if it is clrf nn+1 ; when no voltage is attached bsf channel, ch2 call requestData ; request data from channel 2 movlw 25 movwf del call delay ; 25 msec ADC delay call getData ; get ADC code for positive voltages btfss n+1, 7 goto $+3 clrf n ; set n=0 for negative n, e.g. for input clrf n+1 ; voltages close to 0V movlw LOW 7562 ; checking the range subwf nn, w ; ADC code for negative voltages should not movlw HIGH 7562 ; exceed 7261 (treated as unsigned) movwf tmp btfss STATUS, C incfsz tmp, w subwf nn+1, w btfss STATUS, C goto bin2BCD movlw LOW 7561 ; replace nn with its maximum value movwf nn ; if needed, e.g. if no negative voltage is movlw HIGH 7561 ; connected movwf nn+1 ; in this case 0 will be shown on display bin2BCD movf n, w ; preprocessing the positive voltage code n movwf tmp ; n is at most 13-bit value movf n+1, w movwf tmp+1 ; copy n in tmp bcf STATUS, C rlf n, f rlf n+1, f ; n = 2*n movf tmp, w addwf n, f movf tmp+1, w btfsc STATUS, C incf tmp+1, w addwf n+1, f ; n = 3*n movlw 5 ; add rounding constant addwf n, f btfsc STATUS, C incf n+1, f ; n is ready for BCD conversion movf nn, w ; preprocessing the negative voltage code nn movwf tmp ; nn is at most 13-bit value movf nn+1, w movwf tmp+1 ; copy nn in tmp bcf STATUS, C rlf nn, f rlf nn+1, f ; nn = 2*nn movf tmp, w addwf nn, f movf tmp+1, w btfsc STATUS, C incf tmp+1, w addwf nn+1, f ; nn = 3*nn bcf STATUS, C rrf tmp+1, f rrf tmp, f bcf STATUS, C rrf tmp+1, f rrf tmp, f ; tmp = [nn / 4] btfss STATUS, C goto $+4 incf tmp, f ; rounding off btfsc STATUS, Z incf tmp+1, f movf nn, w ; computing tmp += nn addwf tmp, f movf nn+1, w btfsc STATUS, C incf nn+1, w addwf tmp+1, f ; tmp = 13*nn/4 movlw LOW 24576 movwf nn movlw HIGH 24576 movwf nn+1 ; nn = 24576 movf tmp, w ; computing nn = nn - tmp subwf nn, f movf tmp+1, w btfss STATUS, C incf tmp+1, w subwf nn+1, f movlw 5 ; add rounding constant addwf nn, f btfsc STATUS, C incf nn+1, f ; nn is ready for BCD conversion movlw 0xFF movwf thousands1 movwf thousands2 movwf hundreds1 movwf hundreds2 movwf tens1 movwf tens2 movwf units1 movwf units2 l1 movlw LOW 10000 ; 16-bit subtract subwf n, f movlw HIGH 10000 movwf tmp btfss STATUS, C incfsz tmp, w subwf n+1, f incf thousands1, f btfsc STATUS, C goto l1 movlw LOW 10000 ; restore n addwf n, f movlw HIGH 10000 btfsc STATUS, C movlw (HIGH 10000) + 1 addwf n+1, f l2 movlw LOW 1000 ; 16-bit subtract subwf n, f movlw HIGH 1000 movwf tmp btfss STATUS, C incfsz tmp, w subwf n+1, f incf hundreds1, f btfsc STATUS, C goto l2 movlw LOW 1000 ; restore n addwf n, f movlw HIGH 1000 btfsc STATUS, C movlw (HIGH 1000) + 1 addwf n+1, f l3 movlw 100 ; 16-bit subtract subwf n, f clrw clrf tmp btfss STATUS, C incfsz tmp, w subwf n+1, f incf tens1, f btfsc STATUS, C goto l3 movlw 100 ; restore n addwf n, f l4 movlw 10 subwf n, f incf units1, f btfsc STATUS, C goto l4 l5 movlw LOW 10000 ; processing negative voltages subwf nn, f movlw HIGH 10000 movwf tmp btfss STATUS, C incfsz tmp, w subwf nn+1, f incf thousands2, f btfsc STATUS, C goto l5 movlw LOW 10000 ; restore nn addwf nn, f movlw HIGH 10000 btfsc STATUS, C movlw (HIGH 10000) + 1 addwf nn+1, f l6 movlw LOW 1000 ; 16-bit subtract subwf nn, f movlw HIGH 1000 movwf tmp btfss STATUS, C incfsz tmp, w subwf nn+1, f incf hundreds2, f btfsc STATUS, C goto l6 movlw LOW 1000 ; restore nn addwf nn, f movlw HIGH 1000 btfsc STATUS, C movlw (HIGH 1000) + 1 addwf nn+1, f l7 movlw 100 ; 16-bit subtract subwf nn, f clrw clrf tmp btfss STATUS, C incfsz tmp, w subwf nn+1, f incf tens2, f btfsc STATUS, C goto l7 movlw 100 ; restore nn addwf nn, f l8 movlw 10 subwf nn, f incf units2, f btfsc STATUS, C goto l8 display ; display ADC data in HEX movlw 1 ; digit address movwf dat+1 ; (negative voltages) movf thousands2, w ; btfss STATUS, Z ; drop leading 0 ; call encode7seg btfsc STATUS, Z ; display "-" sign movlw 10 call encode7seg movwf dat call write_MAX7221 movlw 3 ; digit address movwf dat+1 movf hundreds2, w call encode7seg movwf dat bsf dat, DP call write_MAX7221 movlw 8 ; digit address movwf dat+1 movf tens2, w call encode7seg movwf dat call write_MAX7221 movlw 6 ; digit address movwf dat+1 movf units2, w call encode7seg movwf dat call write_MAX7221 movlw 2 ; SECOND NUMBER digit address movwf dat+1 ; (positive voltages) movf thousands1, w btfss STATUS, Z call encode7seg movwf dat call write_MAX7221 movlw 4 ; digit address movwf dat+1 movf hundreds1, w call encode7seg movwf dat bsf dat, DP call write_MAX7221 movlw 7 ; digit address movwf dat+1 movf tens1, w call encode7seg movwf dat call write_MAX7221 movlw 5 ; digit address movwf dat+1 movf units1, w call encode7seg movwf dat call write_MAX7221 goto loop ; endless loop END