Hi everybody:
I'm having troubles trying to communicate a f628a and a DS1820 using the internal pic oscillator @ 48kHz, 3.3V. Communication between them @ 4MHz is successful , but @ 48kHz is not.
My question is : is this possible (communication @ 48kHz)?, or am I doing something wrong?
this is the modificated part (taken from the very usual code)
Thanks in advace for your comments
I'm having troubles trying to communicate a f628a and a DS1820 using the internal pic oscillator @ 48kHz, 3.3V. Communication between them @ 4MHz is successful , but @ 48kHz is not.
My question is : is this possible (communication @ 48kHz)?, or am I doing something wrong?
this is the modificated part (taken from the very usual code)
Code:
;******************************************************************
;* *
;* Dallas/Maxim DS18B20 Temperature Sensor Routines *
;* *
;******************************************************************
OW_HIZ:MACRO
bsf STATUS,RP0 ; bank 1
bsf TRISA,DQ ; set DQ pin as HiZ input
bcf STATUS,RP0 ; bank 0
ENDM ;
OW_LO:MACRO
bcf STATUS,RP0 ; Select Bank 0 of data memory
bcf PORTA, DQ ; Clear the DQ bit
bsf STATUS,RP0 ; Select Bank 1 of data memory
bcf TRISA, DQ ; Make DQ pin an output
bcf STATUS,RP0 ; Select Bank 0 of data memory
ENDM
;
WAIT:MACRO TIME ;
movlw (TIME/5)-1 ; 1 µsec
call WAIT5U ; 2 µsec
ENDM
WAIT5U nop ; 1 µsec
addlw -1 ; 1 µsec
bnz WAIT5U ; 3µsec or 2µsec
return ; 2 µsec
OW_RESET
OW_HIZ
clrf PDByte
OW_LO
;WAIT .500
nop
nop
nop
nop
nop
nop
OW_HIZ ;
;WAIT .70 ;
nop
btfss PORTA,DQ ;
incf PDByte,F ;
;WAIT .430 ;
nop
nop
nop
nop
nop
return ;
;
; RX byte
;
DSRXBYTE
movlw .8 ;
movwf Count ; set bit counter
DSRXLP
OW_LO ; bring DQ low for 6 usecs
nop
;nop
;nop
;nop
;nop
;nop
OW_HIZ ; change to HiZ and wait 4 usecs
nop
;nop
;nop
;nop
movf PORTA,W ; read DQ
andlw 1<<DQ ; mask off the DQ bit
addlw .255 ; C=1 if DQ=1: C=0 if DQ=0
rrf IOByte,F ; Shift C into IOBYTE
;WAIT .50 ; Wait 50µs to end of time slot
nop
decfsz Count,F ; Decrement the bit counter
goto DSRXLP ;
movf IOByte,W ;
return ;
;
; TX byte
;
DSTXBYTE
movwf IOByte ; we send it from IOBYTE
movlw .8 ;
movwf Count ; set bit counter
DSTXLP OW_LO ; drive the line low for 3us
nop
;nop
;nop
rrf IOByte,F
bsf STATUS,RP0 ; bank 1
btfsc STATUS,C ; test LSB of IOBYTE for 1 or 0
bsf PORTA,DQ ; HiZ the line if bit is 1
bcf STATUS,RP0 ; bank 0
;WAIT .60 ; continue driving line for 60µs
nop
OW_HIZ ; release the line for pullup
nop
;nop ; recovery time of 2µs
decfsz Count,F ; decrement the bit counter
goto DSTXLP
return ;
;******************************************************************
;
; get temperature reading
;
GetTemp
call OW_RESET ; send reset signal
btfss PDByte,0 ; DS18B20 found?
return ; no, return, else
movlw h'CC'
call DSTXBYTE ; send 'skip rom' command
movlw h'44'
call DSTXBYTE ; start temperature conversion
ReadSlot
;WAIT .60 ; wait 60-usecs
nop
OW_LO ; start new read slot
OW_HIZ
nop
;nop
;nop
;nop
;nop
btfss PORTA,DQ ; conversion complete '1'?
goto ReadSlot ; no, do another slot, else
;WAIT .60 ; finish read slot period
nop
GetResult
call OW_RESET ; send reset signal
movlw h'CC'
call DSTXBYTE ; send 'skip rom' command
movlw h'BE'
call DSTXBYTE ; send 'read scratchpad' command
call DSRXBYTE
movwf TempL ; save temperature lo
call DSRXBYTE
movwf TempH ; save temperature hi
bcf STATUS,C
rrf TempL,f ; eliminate "decimal" place
returnThanks in advace for your comments