Hello again.

I'm trying to read temperature with DS18B20, using PIC16F84.
Finally I get some data from that sensor, but it works somehow
strange. When slowly heating a sensor, I see readings like this:

22->30->23->31->24->16->25->17->26->18 (celsius)

Real temperatures are those 22,23,24,25 and so on. but those values in
between are wrong. I can not find where i am doing something wrong:(

Here is part of the asm, for beginning I am reading only full degrees,
so i take both data bytes, shift them 4 bits to leave integer only,
and then decode and show it on old LED ascii display HDLU-1414.
Program is based on routines from maxim application note 2420.
May be somebody can see the error:)


go
	clrf	led_adr
	call	hpdl_clear
	movlw	0x1b
	movwf	digits
req_conv
	call	hpdl_clear
	bsf	testout
	CALL	OW_RESET	; reset 1wire
	BTFSS	PDBYTE,0	; 1 = PD received
	GOTO	NOPDPULSE	; if not, error
	MOVLW	SKPROM		
	CALL	DSTXBYTE	; skip ROM
	MOVLW	CONVT
	CALL	DSTXBYTE	; convert temperature
wait_for_ready

	btfss	PORTB,DQ

	goto	wait_for_ready
	CALL	OW_RESET	; reset 1wire
	BTFSS	PDBYTE,0	; 1 = PD received
	GOTO	NOPDPULSE	; error
	MOVLW	SKPROM
	CALL	DSTXBYTE	; Skip ROM
	MOVLW	RDSCR
	CALL	DSTXBYTE	; read scratchpad
	CALL	DSRXBYTE	;
	MOVFW	IOBYTE
	MOVWF	PICMSB		; Put the Current MSB into file PICMSB
	CALL	DSRXBYTE
	MOVFW	IOBYTE
	MOVWF	PICLSB		; Put the Current LSB into file PICLSB
	CALL	DSRXBYTE
	CALL	DSRXBYTE
	CALL	DSRXBYTE
	CALL	DSRXBYTE
	CALL	OW_RESET	; reset 1wire
	BTFSS	PDBYTE,0	; 1 = PD received
	GOTO	NOPDPULSE	; if not, error
	rrf	PICMSB,F
	rrf	PICMSB,F
	rrf	PICMSB,F
	rrf	PICMSB,F	;shift 4 bits R
	movlw	15		;mask for 4 bits
	andwf	PICMSB,F	;leaving 4 bits
	andwf	PICLSB,F	;leaving 4 bits
	rlf	PICLSB,F
	rlf	PICLSB,F
	rlf	PICLSB,F
	rlf	PICLSB,F	;shift 4 bits left
	movfw	PICLSB
	xorwf	PICMSB,W	;join both bytes
	
	movwf	BIN
	call BIN2BCD

	bcf	testout
	call	hpdl_out
	call delay
goto	req_conv



-- 
KPL
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