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Adjust error code values for disconnected sensor
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The existing values are within the operating range of the MAX31850.
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@karlg100
karlg100 committed Jan 2, 2021
1 parent 0d01352 commit ac1eb7f
Showing 1 changed file with 4 additions and 4 deletions.
8 changes: 4 additions & 4 deletions DallasTemperature.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,13 +29,13 @@
#define DS18S20MODEL 0x10 // also DS1820
#define DS18B20MODEL 0x28 // also MAX31820
#define DS1822MODEL 0x22
#define DS1825MODEL 0x3B
#define DS1825MODEL 0x3B // also MAX31850
#define DS28EA00MODEL 0x42

// Error Codes
#define DEVICE_DISCONNECTED_C -127
#define DEVICE_DISCONNECTED_F -196.6
#define DEVICE_DISCONNECTED_RAW -7040
#define DEVICE_DISCONNECTED_C -255

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@bobwolff68

bobwolff68 Jun 7, 2022

This change has created warnings in what was a totally clean build library. And it may also cause real problems in the disconnected case.
int8_t DallasTemperature::getHighAlarmTemp(const uint8_t* deviceAddress)
This function returns an 8-bit signed value who's range is -127 to 128 but the DEVICE_DISCONNECTED_C is now -255 (used to be -127). And so the compiler will convert the -255 to "1" which isn't the intended value and will fool some logic. Can this be fixed/updated?

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@RobTillaart

RobTillaart Jun 7, 2022

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After a quick look I confirm the possible problems. (no test setup run yet).
I assume there is quite some code out there that does check against -127 (hard coded) instead of the CONSTANT.

@bobwolff68
Can you create an issue for this?

Some thoughts

  1. revert the values and accept that they are in range of the MAX31850
  2. create a separate class for MAX31850
  3. create a derived class for MAX31850
  4. replace all int8_t code into int16_t in the library.
#define DEVICE_DISCONNECTED_F -427
#define DEVICE_DISCONNECTED_RAW -32640

// For readPowerSupply on oneWire bus
// definition of nullptr for C++ < 11, using official workaround:
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2 comments on commit ac1eb7f

@milesburton
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I presume the quick fix here is to switch it back to -127? If so I change that quickly enough

@RobTillaart
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@milesburton that is indeed the quick fix.
more elaborate answer in the issue.

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