PIC Microcontoller Radix Math Method

2 digit ASCII decimal to 8 bit Binary

Robert White shares this code:

ASCII 3 digit decimal to 8 bit binary.

CONV_ASCII_HEX
	MOVLW	0X30
	SUBWF	DIGIT2, F
	SUBWF	DIGIT3, F
DIGI1
	SUBWF	DIGIT1, F
	BTFSC	STATUS, Z
	GOTO	X0
	MOVF	DIGIT1, W
	SUBLW	0X02
	BTFSC	STATUS, Z
	GOTO	X200
	MOVF	DIGIT1, W
	SUBLW	0X01
	BTFSC	STATUS, Z
	GOTO	X100
	GOTO	X0
X0
	CLRF	OUT
	GOTO	DIGI2
X100
	MOVLW	0X64
	MOVWF	OUT
	GOTO	DIGI2
X200
	MOVLW	0XC8
	MOVWF	OUT
DIGI2
	MOVLW	0X09
	MOVWF	COUNTN
	MOVF	DIGIT2, W
LOOPN
	ADDWF	DIGIT2, F
	DECFSZ	COUNTN, F
	GOTO	LOOPN
	MOVF	DIGIT2, W
	ADDWF	OUT, F
DIGI3
	MOVF	DIGIT3, W
	ADDWF	OUT, F
	RETURN	 

the three starting digits are in <DIGIT1;DIGIT2;DIGIT3>, and the binary is in OUT. good for use in RS232 terminal applications, which is what I designed it for. Also good for keypad etc.

Comments:

• ; 2 digit ASCII decimal to 8 bit Binary
  ; This how I'd have done it as it saves having any loops - 18 clks
  ; ASCII DIGIT1=(hundreds), DIGIT2=(tens), DIGIT3=(units). The hex value is in OUT.
  ; The routine does not affect any of the ASCII DIGIT values, or need addition registers.
  ; CAUTION: The routine does not test that the ASCII values are valid !
  ; I have just written this code to show the idea, it hasn't been tested in anyway.  
  
  
  CONV_ASCII_HEX
  
  	movlw	0X0F		; Bit pattern to strip off ASCII offset 
  	andwf	DIGIT3, W 	; convert ASCII value to a number (units)
  	movwf	OUT, F		; start the running total (units)
  
  	rlf	DIGIT2, W	; read 2*DIGIT2 doing (tens)
  	andlw	0x1E		; clear ASCII offset + odd bits
  	addwf	OUT, F		; add to running total total 2T + U
  	addwf	OUT, F		; add to running total total 4T + U
  	addwf	OUT, F		; add to running total total 6T + U
  	addwf	OUT, F		; add to running total total 8T + U
  	addwf	OUT, F		; add to running total total 10T + U
  	
  	movlw	'1'		; (Hundred) digit can only usefully be 1 or 2
  	subwf	DIGIT1, W	; test value of DIGIT1 (sets flags)
  	movlw	0x00		; clear value to add to total 
  	btfsc	STATUS, C	; test if result negative ie DIGIT1 was <='0'	 
  	movlw	200		; DIGIT1 was >'0', total needs inc by 100 or 200 
  	btfsc	STATUS, Z	; test if result = '1'
  	movlw	100		; DIGIT1 was = '1' inc total by 100
  	addwf	OUT, F		; add 0, 100 or 200 to total as req
  

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Questions:

• spamdimigavspam at gmail.com asks: " Do you have something about 4 ASCII to 16 bit?" James Newton of Massmind replies: See BCD at /techref/microchip/math/radix/index.htm+

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