16F877, DS18S20 and Serial Comm Problem
I have a very simple PIC program that reads the temperature on a DS18S20 one-wire temperature sensor then send that reading through the USART via serial comm to a VB GUI.
From there VB collects the data via the OnComm event and processes it to the operator.
Problem is, eventually the PIC flips out ans starts sending bad data
Here's the PIC code to collect the temp and send it to the VB GUI:
include "modedefs.bas"
DEFINE OSC 20
DEFINE ADC_BITS 10 ' Set number of bits in result
DEFINE ADC_CLOCK 3 ' Set clock source (3=rc)
DEFINE ADC_SAMPLEUS 50 ' Set sampling time in uS
DEFINE HSER_TXSTA 24H
DEFINE HSER_RCSTA 90H
DEFINE HSER_BAUD 9600
DEFINE HSER_CLROERR
COMMAND VAR BYTE[2]
RESPONSE VAR BYTE[2]
COUNTR VAR BYTE
COUNTC VAR BYTE
DS18S20F VAR WORD
DS18S20 VAR WORD
TEMP1 VAR PORTB.7
'I/O CONFIGURATION
ADCON0 = %10000001
ADCON1 = %11000100 '%11000000
TRISA=%10011111
TRISB=%00000000
TRISC=%11001011
TRISD=%11110001 '11110001
TRISE=%00000000
'USART SETTINGS
PIE1=%01110000
RCSTA=%10010000 'ENABLE SERIAL PORT AND RECEPTION
TXSTA=%00100100
MAIN:
GOSUB CommandIN
GoTo MAIN
CommandIN:
If PIR1.5=1 then
HSERIN ,2000, TIMEOUT, [STR COMMAND\2] 'IF THERE IS SOMETHING IN THE RECIEVE REGISTER STORE IT IN "COMMAND"
GOSUB EXECUTE
TIMEOUT:'HSEROUT ["TIMEOUT"]
ENDIF
RETURN
'***** EXECUTE THE INCOMING COMMAND BASED ON THE CHARACTERS RECIEVED ****
EXECUTE:
IF COMMAND(0)="T" THEN
GOSUB READTEMP
RESPONSE(0)=COMMAND(0)
'HSEROUT [RESPONSE(0), DEC (DS18S20F/100), ".", DEC1 (DS18S20F),"X"]
HSEROUT [RESPONSE(0), DEC (DS18S20F),"X"]
ENDIF
RETURN
READTEMP:
LOW TEMP1 'initialize DS18S20
PAUSEUS 500 'wait for return pulse
TRISB.7=1 'set pin as input to get temp reading
PAUSEUS 100
IF TEMP1=1 THEN
DS18S20F=999 'VB error code signaling no sensor connected
RETURN
ENDIF
PAUSEUS 400
OWOUT TEMP1, 1, [$CC, $44] ' $CC-SKIP SEARCHING FOR MULTIPLE DS18S20, $44-START
TEMPERATURE CONVERSION
WAITFORCONVERSION:
OWIN TEMP1, 4, [COUNTR] 'CHECK FOR STILL BUSY CONVERTING SIGNAL
IF COUNTR=0 THEN WAITFORCONVERSION
OWOUT TEMP1, 1, [$CC, $BE] 'READ THE TEMPERATURE
OWIN TEMP1, 0, [DS18S20.LOWBYTE, DS18S20.HIGHBYTE, SKIP 4, COUNTR, COUNTC]
DS18S20=((DS18S20>>1*100)-25)+(((COUNTC-COUNTR)*100)/COUNTC)
DS18S20F=(DS18S20 */ 461)+3200 'CALCULATE TEMP IN DEGREES F, NOT VALID FOR NEGATIVE TEMP
RETURN
'*****************************************
Now, the problem is that after about 60 minutes of collecting temp readings and sending them to VB the PIC or temp sensor flips out and starts sending the same digit over and over. Here is a sampling of the data received from the pic (VB adds the date/time stamp):
T7228X 4/21/2004 9:55:06 AM
T744X 4/21/2004 10:00:06 AM
T741X 4/21/2004 10:05:06 AM
T735X 4/21/2004 10:10:07 AM
T742X 4/21/2004 10:15:07 AM
T763X 4/21/2004 10:20:07 AM
T729X 4/21/2004 10:25:07 AM
T728X 4/21/2004 10:30:07 AM
T724X 4/21/2004 10:35:07 AM
T769X 4/21/2004 10:40:07 AM
T762X 4/21/2004 10:45:07 AM
T60X 4/21/2004 10:50:13 AM "**********This is where things go wrong******************
T7228X80 4/21/2004 10:55:13 AM
008X 4/21/2004 11:00:13 AM
008X.888 4/21/2004 11:05:13 AM
008X.888.888 4/21/2004 11:10:13 AM
008X.888.888.888 4/21/2004 11:15:13 AM
008X.888.888.888.888 4/21/2004 11:20:13 AM
008X.888.888.888.888.888 4/21/2004 11:25:13 AM '*VB clears the buffer and it starts over
.888 4/21/2004 11:30:13 AM
.888.888 4/21/2004 11:35:13 AM
.888.888.888 4/21/2004 11:40:13 AM
and so on, and so forth.....
Any idea what is going on? Where do I start trouble shooting?
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