This is the code I use for calculating the CRC from the Dallas 18B20 temperature sensor. The only difference I can notice is the locations of the << and >> in the two code. Can you give me an example of how your code is used cause I'm still a little fuzzy on what data does where. I know the CRC value byte is the third byte but not sure what bytes are used to calculate the CRC to compare to this value.
Code:------------------------ Calculate the CRC from Byte 9 ------------------------ GetCRC: for x = 0 to 7 databyte = dq[x] gosub CalcCRC next x if dq[8] <> crccalc then sensorerror = 1 else sensorerror = 0 endif crccalc = 0 return '--------------------- CRC Bit Calcuation Method ------------------------------- CalcCRC: for i = 0 to 7 databit = crccalc.0 ^ databyte.0 databyte = databyte >> 1 if databit = 0 then Shift crccalc = crccalc ^ $18 shift: crccalc = crccalc >> 1 crccalc.7 = databit next i returnCode:'------------------ Read SHT71 Temperature / Humidity Sensor ------------------- ReadSHT71: gosub Initialize Sensorcmd = ReadTemp gosub readsensor if result => 4000 then tempC = result - 4000 SignC = 160 else tempC = 4000 - result SignC = "-" endif gosub ConvertToKelvin gosub ConvertToFahrenheit gosub Initialize Sensorcmd = ReadHumidity gosub readsensor '--------------------- Calculate Relative Humidity ----------------------------- w = result * 405 w = div32 100 x = result * result x = div32 1000 x = x * 28 x = div32 100 RHLinear = w - x - 400 '---------- Calculate Relative Humidity with Temperature Compensation ---------- w = (8 * result + 1000) / 10 if SignC = 160 then if tempC > 2500 then x = (tempC - 2500) * w x = div32 100 RHTempComp = RHLinear + x / 100 else x = (2500 - temp) * w x = div32 100 RHTempComp = RHLinear - x / 100 endif else x = (2500 + tempC) * w x = div32 10000 RHTempComp = RHLinear - x endif sleep 1 return '---------------------------- Initialize the Sensor ---------------------------- Initialize: high DataPin low clk for i = 1 to 10 high clk pause 1 low clk pause 1 next i call TransferStart return '---------------------------- Get Data from Sensor ----------------------------- ReadSensor: gosub TransferStart gosub WaitSensor shiftout DataPin,clk,1,[Sensorcmd\8] ' Send command byte input DataPin ' Wait for acknowledge low clk while DataPin = 1 wend pulsout clk,10 ' Send acknowledge while DataPin = 0 wend while DataPin = 1 ' Wait for conversion to complete wend low clk shiftin DataPin,clk,0,[result.byte1\8] ' Get the first byte, 8 bits low DataPin pulsout clk,10 ' Send acknowledge shiftin DataPin,clk,0,[result.byte0\8] ' Get the second byte, 8 bits low DataPin pulsout clk,10 ' Send acknowledge shiftin DataPin,clk,0,[crc\8] ' Get third byte, 8 bits, CRC high DataPin pulsout clk,10 ' Send acknowledge input DataPin ' End of Transmission input clk return '---------------------------- Start Transfer ----------------------------------- TransferStart: high clk pause 1 low DataPin pause 1 low clk pause 1 high clk pause 1 high DataPin pause 1 low clk return '---------------------------- Wait for Sensor ---------------------------------- WaitSensor: result = 4096 Loop: result = result - 1 if DataPin && result.bit11 then Loop return '-------------------------- Convert to Kelvin ---------------------------------- ConvertToKelvin: if signC = "-" then tempk = 27315 - temp else tempk = temp + 27315 endif return ConvertToFahrenheit: if SignC = 160 then SignF = 160 dummy = TempC * 18 TempF = div32 10 TempF = TempF + 3200 else TempF = (tempc + 5000) * 900 TempF = DIV32 500 if TempC => 1778 and SignC = "-" then TempF = TempF - 12200 SignF = "-" else TempF = 12200 - TempF SignF = 160 endif endif return
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