BCD Addition
This project shows the BCD addition process using PIC16C55. To simulate this circuit, initially activate Mixed Mode simulator from the Schematic Editor window. Simulation can be performed by selecting Run Transient analysis (Oscillograph) from Simulation menu.
The circuit contains a PIC16C55 chip, voltage source, 74LS245,Octal 3-state bus transceiver, 7404 NOT gate. HPDL-1414 Four-Character Alphanumeric Display.
PIC 16C55 has only two 8 bit port and one 4 bit port. This circuit require two 8 bit input and one 16 bit out put .For implementing this a network of 74245 is designed according to the control pins DIR1, G/INB, DIR2, G/INC from PORTA. PORTB and PORTC act as input port or output port.
BCD number 1 is read through PORT B and BCD number 2 is through PORTC by setting 74245 networks in input mode.
HPDL 1414 control signals D0, D1, D2, D3 are given through PORTB and A0, A1, D4, D5, D6, WR are given through PORT C by setting 74245 networks in output mode. HPDL1414 display shows result of BCD addition.
The source code written either in Assembly language can be viewed from the code editor window
The program is as shown:
#include p16c5x.inc ; processor specific variable definitions
;***** VARIABLE DEFINITIONS
TEMP_VAR UDATA
bcd1 res 1 ;bcd1 variable declaration
bcd2 res 1 ;bcd2 variable deTEMP_VAR UDATA
sum res 1 ;sum variable declaration
carry res 1 ;carry variable declaration
sum_lsb res 1 ;sum_lsb variable declaration
sum_msb res 1 ;sum_msb variable declaration
dig0 res 1 ;dig0 variable declaration
dig1 res 1 ;dig1 variable declaration
dig2 res 1 ;dig2 variable declaration
dig3 res 1 ;dig3 variable declaration
control res 1 ;control variable declaration
;**********************************************************************
reset_vector code 0x1FF ; processor reset vector
goto start
MAIN code 0x000
start
;port reading
clrw ;clear accumulator
tris PORTA ;Set port A as output
;set 74245 as output mode
movlw 0x00 ;move literal value to accumulator
movwf PORTA ;move accumulator to port A
movlw 0xff ;move literal value to accumulator
tris PORTB ;Set port B as input
movf PORTB,0 ;move port B to accumulator
movwf bcd1 ;move accumulator to bcd1
movlw 0xff ;move literal value to accumulator
tris PORTC ;Set port C as input
movf PORTC,0 ;move port C to accumulator
movwf bcd2 ;move accumulator to bcd2
clrw ;clear accumulator
movwf carry ;move accumulator to carry
;add bcd and bcd2
movf bcd2,0 ;move bcd2 to accumulator
addwf bcd1,0 ;add accumulator and bcd1 and result in accumulator
movwf sum ;move accumulator to sumlsb
movwf sum_lsb ;move accumulator to sum_lsb
movwf sum_msb ;move accumulator to sum_msb
; if carry bit is 1 set carry
btfsc STATUS,0 ;check carry = 0 ,skip if yes
bsf carry,0 ;set carry as 1
;check dc = 1 if true then call add6
btfsc STATUS,1 ;check dc = 0 ,skip if yes
goto add6 ;goto add6
;masking upper nibble of sum_lsb
movlw 0x0f ;move literal value to accumulator
andwf sum_lsb,1 ;AND sum_lsb with accumulator and result in sumlsb_lsb
;check sum_lsb greater than 9
movlw 0x9 ;move literal value to accumulator
subwf sum_lsb,0 ;subtract 9 from sum_lsb result in accumulator
;if cy = 0 then it is sum_lsb is less than 9
;if sum_lsb grater than 9 add6 to lsb
btfsc STATUS,0 ; skip if carry is zero
goto add6 ;goto add6
carrycheck
btfsc carry,0 ;check carry = 0 ,skip if yes
goto add6_msb ;got add6_msb
;masking lower nibble of sum_msb and swap the result
movlw 0xf0 ;move literal value to accumulator
andwf sum_msb,1 ;AND sum_msb with accumulator and resulT in sumlsb_lsb
swapf sum_msb,1 ;swap sum_msb and result in sum_msb
;check sum_msb is greater than 9
movlw 0x9 ;move literal value to accumulator
subwf sum_msb,0 ;subtract 9 from sum_lsb result in accumulator
btfsc STATUS,0 ; skip if carry is zero
goto add6_msb ; goto add6_msb
goto repeat ;ends
;add 6 to sum
add6 movlw 0x6 ;move literal value to accumulator
addwf sum,1 ;add accumulator with sum result in sum_lsb
btfsc STATUS,0 ;check carry = 0 ,skip if yes
bsf carry,0 ;set carry as 1
goto carrycheck ;goto carry check
;add 60 to sum
add6_msb movlw 0x60 ;move literal value to accumulator
addwf sum,1 ;add accumulator with sum result in sum
btfsc STATUS,0 ;check carry = 0 ,skip if yes
bsf carry,0 ;set carry as 1
;end of conversion
;hpdl 1414 implementation ----------- 74245 as output mode
repeat movlw 0xf ;move literal value to accumulator
movwf PORTA ;move accumulator TO port A
movlw 0x00 ;move literal value to accumulator
tris PORTB ;Set PORT B as output
movlw 0x00 ;move literal value to accumulator
tris PORTC ;Set PORT C as output
;display of DIG0
;Set 74245 in output mode
;separation of zeroth digit
movlw 0x0f ;move literal value to accumulator
andwf sum,0 ;AND sum with accumulator and store the output in accumulator
movwf dig0 ;move accumulator to dig0
;check digit is greater than 9
movlw 0x09 ;move literal value to accumulator
subwf dig0,0 ;subtract 9 from dig0 and result in accumulator
btfss STATUS, 0 ;skip if carry flag is 1
goto nochange ;goto nochange
btfsc STATUS,2 ;skip if zero flag is zero ;ie result is non zero
goto nochange ;goto nochange
movlw 0x09 ;move literal value to accumulator
subwf dig0,1 ;subtract 9 from dig0 and result in dig0
movlw 0x13 ;move literal value to accumulator
movwf control ;move control to accumulator
goto porting0 ;goto porting 0
nochange movlw 0x0f ;move literal value to accumulator
movwf control ;move control to accumulator
porting0 movf dig0,0 ;move dig0 value to accumulator
movwf PORTB ;move accumulator to portB
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
movlw 0xff ;move literal value to accumulator
movwf control ;move control to accumulator
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
;zeroth digit complete
;first digit
;separation of first digit
movlw 0xf0 ;move literal value to accumulator
andwf sum,0 ;AND sum with accumulator and output in accumulator
movwf dig1 ;move accumulator to dig1
swapf dig1,1 ;swap and result in dig1
;check digit is greater than 9
movlw 0x09 ;move literal value to accumulator
subwf dig1,0 ;subtract 9 from dig1 and result in accumulator
btfss STATUS, 0 ;skip if carry flag is 1
goto nochange1 ;goto nochange1
btfsc STATUS,2 ;skip if zero flag is zero, ie result is non zero
goto nochange1 ;goto nochange1
movlw 0x09 ;move literal value to accumulator
subwf dig1,1 ;subtract 9 from dig1 and result in dig1
movlw 0x12 ;move literal value to accumulator
movwf control ;move control to accumulator
goto porting1 ;goto porting 1
nochange1 movlw 0x0e ;move literal value to accumulator
movwf control ;move control to accumulator
porting1 movf dig1,0 ;move dig1 value to accumulator
movwf PORTB ;move accumulator to portB
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
movlw 0xff ;move literal value to accumulator
movwf control ;move control to accumulator
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
;separation of second digit
movlw 0x0f ;move literal value to accumulator
andwf carry,0 ;AND carry with accumulator and output in accumulator
movwf dig2 ;move accumulator to dig2
;check digit is greater than 9
movlw 0x09 ;move literal value to accumulator
subwf dig2,0 ;subtract 9 from dig2 and result in accumulator
btfss STATUS, 0 ;skip if carry flag is 1
goto nochange2 ;goto nochange2
btfsc STATUS,2 ;skip if zero flag is zero, ie result is non zero
goto nochange2 ;goto nochange2
movlw 0x09 ;move literal value to accumulator
subwf dig2,1 ;subtract 9 from dig2 and result in dig2
movlw 0x11 ;move literal value to accumulator
movwf control ;move control to accumulator
goto porting2 ;goto porting 2
nochange2 movlw 0x0d ;move literal value to accumulator
movwf control ;move control to accumulator
porting2 movf dig2,0 ;move dig2 value to accumulator
movwf PORTB ;move accumulator to portB
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
movlw 0xff ;move literal value to accumulator
movwf control ;move control to accumulator
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
;second digit complete
;third digit
;separation of third digit
movlw 0xf0 ;move literal value to accumulator
andwf carry,0 ;AND carry with accumulator and output in accumulator
movwf dig3 ;move accumulator to dig3
swapf dig3,1 ;swap and result in dig3
;check digit is greater than 9
movlw 0x09 ;move literal value to accumulator
subwf dig3,0 ;subtract 9 from dig3 and result in accumulator
btfss STATUS, 0 ;skip if carry flag is 1
goto nochange3 ;goto nochange3
btfsc STATUS,2 ;skip if zero flag is zero, ie result is non zero
goto nochange3 ;goto nochange3
movlw 0x09 ;move literal value to accumulator
subwf dig3,1 ;subtract 9 from dig3 and result in dig3
movlw 0x10 ;move literal value to accumulator
movwf control ;move control to accumulator
goto porting3 ;goto porting 3
nochange3 movlw 0x0c ;move literal value to accumulator
movwf control ;move control to accumulator
porting3 movf dig3,0 ;move dig3 value to accumulator
movwf PORTB ;move accumulator to portB
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
movlw 0xff ;move literal value to accumulator
movwf control ;move control to accumulator
movf control,0 ;move control value to accumulator
movwf PORTC ;move accumulator to port C
repeat2 goto repeat2 ;infinte loop
end ; directive end of program
The source code in the code editor window has to be compiled after making any modifications
(editing). Also the code can be debugged during simulation.