;------------------------------------------------------------------------------------------------------------------------ ; Source code for the PIC16F873A based Capacitance Meter. (5pF to 2500uF range) ;------------------------------------------------------------------------------------------------------------------------ ; **Analog Pinouts ; Vin- - RA0, Channel 0. ; Vin+ - RA3, Channel 3. ; ; **Capacitance (Cx) Charge Controller. (Active Low) ; Low Range - RB4 ; High Range - RB3 ; ; **Push Buttons for Calibration. ; Save Button - RB5, Active Low ; + Button - RB6, Active Low ; - Button - RB7, Active Low ; ; **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=16F873A INCLUDE "p16f873a.inc" ; ERRORLEVEL -302 __CONFIG _PWRTE_OFF & _HS_OSC & _WDT_OFF & _WRT_OFF & _LVP_OFF & _BODEN_OFF; configuration switches CBlock 0x20 visdelay N FIXDELAY ; Delay registers. fractHi offsetsub ; Corrective calibration value. pointer ; Message character pointer. DIVIDENDHI DIVIDENDLO DIVISORHI DIVISORLO QUOTIENTHI QUOTIENTLO REMAINDERHI REMAINDERLO COUNT ; 16 bit divide method registers. digit0 digit1 digit2 digit3 digit4 digit5 ; Individual display digit registers. EndC org 0x00 nop ; Reserved for ICD II. goto start start call initports ; Initialize the PORTs. call setupTMR1 ; Setup Timer1 module. call INITLCD ; Initializes LCD. call dischargecap ; Discharge Cx and enable the comparator module. call dispstartmsg ; Displays the default start message. loadeeprom movlw 0x00 ; 0x00 of EEPROM holds offsetsub corrective calibration value. call eepromread ; Read data pointed at address 0x00. movwf offsetsub ; Load data into offsetsub. main btfss PORTB, 6 ; Check if either of RB6 or RB7 buttons were pushed, incf offsetsub, f ; if they were, adjust the offset subtractor accordingly. btfss PORTB, 7 decf offsetsub, f btfsc PORTB, 5 goto sampling banksel EEADR ; Select location 0x00 of EEPROM. movlw 0x00 movwf EEADR banksel EEDATA movf offsetsub, w ; Write calibrated offset data to 0x00. movwf EEDATA call eepromwrite ; Initiate EEPROM write. call dispsavemsg ; Display saving message. call visualdelay ; Visual delay for viewer. sampling call sampleLo ; Begin sampling Cx, cycles every 255ms. goto main ;------------------------------------------------------------------------------------------------------------------------ ; Subroutine to initialize the PORTs as Inputs or Outputs. ;------------------------------------------------------------------------------------------------------------------------ initports banksel TRISA ; Select TRISA, B, and C banks. movlw b'11111111' ; Define PORTA as Inputs. movwf TRISA movlw b'11100000' ; RB5 to RB7 are inputs, the rest are outputs. movwf TRISB movlw b'00000000' ; All PORTC pins are output. movwf TRISC banksel PORTA ; Select PORTA bank. clrf PORTB ; Clear PORTB and PORTC bits. clrf PORTC bsf PORTB, 4 ; Set RB4 and RB3 to inhibit charging of Cx. bsf PORTB, 3 return ;------------------------------------------------------------------------------------------------------------------------ ; Setup the Timer1 Module. ;------------------------------------------------------------------------------------------------------------------------ setupTMR1 banksel T1CON movlw b'00000000' ; Disable TMR1, 1:1 Prescale, Clock = Fosc/4, OSC off. movwf T1CON return ;------------------------------------------------------------------------------------------------------------------------ ; Discharges Cx and (Re)Initializes Comparator. ;------------------------------------------------------------------------------------------------------------------------ dischargecap banksel CMCON movlw b'00000111' ; OFF Comparators. movwf CMCON banksel PORTB call DELAY20 ; 10us delay for settling time. banksel ADCON1 movlw b'00001110' ; pin RA0 as analog and RA3 as digital. (Maybe not needed?) movwf ADCON1 banksel TRISA bcf TRISA, 3 ; RA3 as output. banksel PORTA bcf PORTA, 3 ; Clear RA3 to discharge Cx. movlw d'255' ; Delay Time to discharge Cx completely. About 255ms. call NDELAY movlw d'255' call NDELAY movlw d'255' call NDELAY movlw d'255' call NDELAY movlw d'255' call NDELAY banksel TRISA bsf TRISA, 3 ; RA3 as input. banksel ADCON1 movlw b'00000000' ; Pin RA0 and RA3 as analog. (Maybe not needed?) movwf ADCON1 banksel CMCON ; Initialize Comparator Module as One Independent Comparator with Output. movlw b'00000001' movwf CMCON banksel PORTB call DELAY20 ; 10us delay for settling time. 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'00001100' ; Display ON, Cursor OFF, Blinking OFF 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 ;------------------------------------------------------------------------------------------------------------------------ ; Visual delay subroutine. ;------------------------------------------------------------------------------------------------------------------------ visualdelay movlw d'20' movwf visdelay seetemp movlw 0xFF call NDELAY decfsz visdelay, 1 goto seetemp 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 ; 20us fixed delay NOTDONE20 DECFSZ FIXDELAY, 1 ; Decrement of FIXDELAY GOTO NOTDONE20 ; If 50us isn't up go back to NOTDONE20 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 ;------------------------------------------------------------------------------------------------------------------------ ; 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 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 ;------------------------------------------------------------------------------------------------------------------------ ; Samples the capacitance charge time. ;------------------------------------------------------------------------------------------------------------------------ sampleLo call dischargecap ; Discharge Cx. banksel TMR1H bcf PIR1, TMR1IF ; Clear TMR1 interrupt flag. clrf TMR1H ; Clear Timer1 values. clrf TMR1L banksel T1CON movlw b'00000000' ; Prescale 1:1, TMR1 Off. movwf T1CON bcf PORTB, 4 ; Clear RB4 to energize Cx. bsf T1CON, 0 ; Enable the Timer1 to measure charge time. waitcharge banksel CMCON btfss CMCON, C1OUT ; Check if VCx > 0.632Vdd? goto timeoutchk sampleLodone banksel T1CON bcf T1CON, 0 ; Disable TMR1 to get time reading. bsf PORTB, 4 ; Stop charging Cx. goto computeLo timeoutchk banksel PIR1 btfss PIR1, TMR1IF ; Check if TMR1 has overflow? goto waitcharge bcf PIR1, TMR1IF ; Clear TMR1 interrupt flag. bsf PORTB, 4 ; Stop charging Cx. goto sampleHi computeLo banksel TMR1H movf TMR1H, w ; Math and display routines here. movwf DIVIDENDHI movf TMR1L, w movwf DIVIDENDLO clrf DIVISORHI ; Divides Measured time by 2. movlw d'2' movwf DIVISORLO call divide16 movf offsetsub, w ; Calibration corrections. subwf QUOTIENTLO, f call displayres ; Display non-fractional result. call displayLofract ; Display fractional result. return sampleHi call dischargecap ; Discharge Cx. banksel T1CON bcf T1CON, 0 ; Disable TMR1 clrf TMR1H ; Clear TMR1 values. clrf TMR1L banksel T1CON movlw b'00110000' ; Prescale 1:8, TMR1 Off. movwf T1CON bcf PIR1, TMR1IF ; Clear TMR1 Interrupt flag. bcf PORTB, 3 ; Clear RB3 to energize Cx. bsf T1CON, 0 ; Enable Timer1 to measure charge time. waitcharge2 banksel CMCON btfss CMCON, C1OUT ; Check if VCx > 0.632Vdd? goto timeoutchk2 sampleHidone banksel T1CON bcf T1CON, 0 ; Stop TMR1 to get time reading. bsf PORTB, 3 ; Stop charging Cx. goto computeHi timeoutchk2 banksel PIR1 btfss PIR1, TMR1IF ; Check if TMR1 has overflow? goto waitcharge2 bcf PIR1, TMR1IF ; If yes, clear TMR1 interrupt flag. bsf PORTB, 3 ; Stop charging Cx. call disperrormsg ; Then display Error message. return computeHi banksel TMR1H movf TMR1H, w ; Math and display routines here. movwf DIVIDENDHI movf TMR1L, w movwf DIVIDENDLO clrf DIVISORHI movlw d'25' movwf DIVISORLO ; Divides measured time by 25. (8us/200 Ohm = 1/25) call divide16 movf REMAINDERLO, w movwf fractHi call displayres call displayHifract return ;------------------------------------------------------------------------------------------------------------------------ ; Displays the default message on line 1 of LCD. ;------------------------------------------------------------------------------------------------------------------------ dispstartmsg movlw 'P' call PUTCHAR movlw 'I' call PUTCHAR movlw 'C' call PUTCHAR movlw 'C' call PUTCHAR movlw 'a' call PUTCHAR movlw 'P' call PUTCHAR movlw 'M' call PUTCHAR movlw 'e' call PUTCHAR movlw 't' call PUTCHAR movlw 'e' call PUTCHAR movlw 'r' call PUTCHAR movlw ' ' call PUTCHAR movlw 'v' call PUTCHAR movlw '1' call PUTCHAR movlw '.' call PUTCHAR movlw '0' call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; Displays the error message when Cx is out of range. ;------------------------------------------------------------------------------------------------------------------------ disperrormsg call nextline movlw 'O' call PUTCHAR movlw 'u' call PUTCHAR movlw 't' call PUTCHAR movlw ' ' call PUTCHAR movlw 'o' call PUTCHAR movlw 'f' call PUTCHAR movlw ' ' call PUTCHAR movlw 'R' call PUTCHAR movlw 'a' call PUTCHAR movlw 'n' call PUTCHAR movlw 'g' call PUTCHAR movlw 'e' call PUTCHAR movlw '!' call PUTCHAR movlw ' ' call PUTCHAR movlw ' ' call PUTCHAR movlw ' ' call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; Displays save message when RB5 button is pushed. ;------------------------------------------------------------------------------------------------------------------------ dispsavemsg call nextline movlw 'S' call PUTCHAR movlw 'a' call PUTCHAR movlw 'v' call PUTCHAR movlw 'i' call PUTCHAR movlw 'n' call PUTCHAR movlw 'g' call PUTCHAR movlw ' ' call PUTCHAR movlw 'S' call PUTCHAR movlw 't' call PUTCHAR movlw 'a' call PUTCHAR movlw 't' call PUTCHAR movlw 'e' call PUTCHAR movlw '.' call PUTCHAR movlw '.' call PUTCHAR movlw '.' call PUTCHAR movlw '.' call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; 16 bit divide method by Andy Warren. ;------------------------------------------------------------------------------------------------------------------------ divide16 CLRF REMAINDERLO ;CLEAR THE REMAINDER. CLRF REMAINDERHI ; MOVLW d'16' ;WE'RE DIVIDING BY A 16-BIT DIVISOR. MOVWF COUNT ; DIVLOOP RLF DIVIDENDLO, f ;SHIFT DIVIDEND LEFT 1 BIT INTO RLF DIVIDENDHI, f ;REMAINDERHI:REMAINDERLO. RLF REMAINDERLO, f ; RLF REMAINDERHI, f ; MOVF DIVISORHI,W ;COMPARE THE DIVISOR TO THE PORTION OF THE SUBWF REMAINDERHI,W ;DIVIDEND THAT'S BEEN SHIFTED INTO REMHI. BNZ CHECKLESS ;IF THE TWO HI-BYTES AREN'T THE SAME, JUMP ;AHEAD. MOVF DIVISORLO,W ;OTHERWISE, WE HAVE TO COMPARE THE SUBWF REMAINDERLO,W ;LO-BYTES. CHECKLESS BNC NOSUB ;IF THE SHIFTED PORTION OF THE DIVIDEND WAS ;LESS THAN THE DIVISOR, JUMP AHEAD. MOVF DIVISORLO,W ;OTHERWISE, REMAINDER = REMAINDER - DIVISOR. SUBWF REMAINDERLO, f ; MOVF DIVISORHI,W ; SKPC ; INCFSZ DIVISORHI, f ; SUBWF REMAINDERHI, f ; (CARRY'S ALWAYS SET AT THIS POINT.) NOSUB RLF QUOTIENTLO, f ;IF WE JUST SUBTRACTED, SHIFT A "1" INTO RLF QUOTIENTHI, f ;THE QUOTIENT. OTHERWISE, SHIFT A "0". DECFSZ COUNT, f ;HAVE WE SHIFTED ENOUGH BITS? GOTO DIVLOOP ;IF NOT, LOOP BACK. RETURN ;------------------------------------------------------------------------------------------------------------------------ ; Display non-fractional result. ;------------------------------------------------------------------------------------------------------------------------ displayres call nextline ; Cursor to line 2. movlw A'C' ; Displays "Cx is xxxxx.xxpF or uF" call PUTCHAR movlw A'x' call PUTCHAR movlw A' ' call PUTCHAR movlw A'i' call PUTCHAR movlw A's' call PUTCHAR movlw A' ' call PUTCHAR call numsplit addlw d'48' movwf digit0 call numsplit addlw d'48' movwf digit1 call numsplit addlw d'48' movwf digit2 call numsplit addlw d'48' movwf digit3 call numsplit addlw d'48' movwf digit4 call numsplit movf digit4, w call PUTCHAR movf digit3, w call PUTCHAR movf digit2, w call PUTCHAR movf digit1, w call PUTCHAR movf digit0, w call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; Display Low Cx Fractional Values. ;------------------------------------------------------------------------------------------------------------------------ displayLofract movlw A'.' ; Displays .00pF call PUTCHAR movlw A'0' call PUTCHAR movlw A'0' call PUTCHAR movlw b'11100110' ; pico sign. call PUTCHAR movlw A'F' call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; Display Hi Cx Fractional Values. ;------------------------------------------------------------------------------------------------------------------------ displayHifract movlw A'.' call PUTCHAR bcf STATUS, C ; Multiply the remainder of Cx Hi by 4 to convert it to fractional value. rlf fractHi, f bcf STATUS, C rlf fractHi, f clrf DIVIDENDHI movf fractHi, w movwf DIVIDENDLO clrf DIVISORHI movlw d'10' movwf DIVISORLO call divide16 movf QUOTIENTLO, w ; Display the fractional values. addlw d'48' call PUTCHAR movf REMAINDERLO, w addlw d'48' call PUTCHAR movlw b'11100100' ; micro sign. call PUTCHAR movlw A'F' call PUTCHAR return ;------------------------------------------------------------------------------------------------------------------------ ; Number splitter. ;------------------------------------------------------------------------------------------------------------------------ numsplit movf QUOTIENTHI, w ; Get the remainder number, i.e. the first digit from the left. movwf DIVIDENDHI movf QUOTIENTLO, w movwf DIVIDENDLO clrf DIVISORHI movlw d'10' movwf DIVISORLO call divide16 movf REMAINDERLO, w return ;------------------------------------------------------------------------------------------------------------------------ ; EEPROM Reader. ;------------------------------------------------------------------------------------------------------------------------ eepromread banksel EEADR ; Select bank for EEADR. movwf EEADR ; Pass address to EEADR. banksel EECON1 ; Select bank for EECON1. bcf EECON1, EEPGD ; Select data memory. bsf EECON1, RD ; Read the value on the specified address. banksel EEDATA ; Select bank for EEDATA. movf EEDATA, w ; Pass data to WREG. banksel PORTC ; Select bank 0. return ;------------------------------------------------------------------------------------------------------------------------ ; EEPROM Writer. ;------------------------------------------------------------------------------------------------------------------------ eepromwrite banksel EECON1 ; Select bank for EECON1 and EECON2. bcf EECON1, EEPGD ; Select data memory. bsf EECON1, WREN ; Enable EEPROM write. movlw 0x55 ; Required sequences. movwf EECON2 movlw 0xAA movwf EECON2 bsf EECON1, WR ; Set WR bit to begin write. bcf EECON1, WREN ; Disable further writes. btfsc EECON1, WR ; Check if write is completed. goto $-1 ; If no, wait up. return ; If yes, return. ;------------------------------------------------------------------------------------------------------------------------ ; End of Programme. ;------------------------------------------------------------------------------------------------------------------------ end