fix: Restored DS18S20 support

milesburton · Jan 21, 2025 · 4839194 · 4839194
1 parent 3cfcb26
commit 4839194
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Showing 4 changed files with 38 additions and 3 deletions.
diff --git a/DallasTemperature.cpp b/DallasTemperature.cpp
@@ -36,6 +36,10 @@ extern "C" {
 
 #define NO_ALARM_HANDLER ((AlarmHandler *)0)
 
+// DSROM FIELDS
+#define DSROM_FAMILY    0
+#define DSROM_CRC       7
+
 DallasTemperature::DallasTemperature() {
     _wire = nullptr;
     devices = 0;
@@ -554,6 +558,37 @@ int32_t DallasTemperature::calculateTemperature(const uint8_t* deviceAddress, ui
                        | neg;
     }
 
+  /*
+   DS1820 and DS18S20 have a 9-bit temperature register.
+
+   Resolutions greater than 9-bit can be calculated using the data from
+   the temperature, and COUNT REMAIN and COUNT PER °C registers in the
+   scratchpad.  The resolution of the calculation depends on the model.
+
+   While the COUNT PER °C register is hard-wired to 16 (10h) in a
+   DS18S20, it changes with temperature in DS1820.
+
+   After reading the scratchpad, the TEMP_READ value is obtained by
+   truncating the 0.5°C bit (bit 0) from the temperature data. The
+   extended resolution temperature can then be calculated using the
+   following equation:
+
+                                    COUNT_PER_C - COUNT_REMAIN
+   TEMPERATURE = TEMP_READ - 0.25 + --------------------------
+                                           COUNT_PER_C
+
+   Hagai Shatz simplified this to integer arithmetic for a 12 bits
+   value for a DS18S20, and James Cameron added legacy DS1820 support.
+
+   See - http://myarduinotoy.blogspot.co.uk/2013/02/12bit-result-from-ds18s20.html
+   */
+
+  if ((deviceAddress[DSROM_FAMILY] == DS18S20MODEL) && (scratchPad[COUNT_PER_C] != 0)) {
+    fpTemperature = (((fpTemperature & 0xfff0) << 3) - 32
+                    + (((scratchPad[COUNT_PER_C] - scratchPad[COUNT_REMAIN]) << 7)
+                       / scratchPad[COUNT_PER_C])) | neg;
+  }
+
     return fpTemperature;
 }
 

diff --git a/DallasTemperature.h b/DallasTemperature.h
@@ -1,7 +1,7 @@
 #ifndef DallasTemperature_h
 #define DallasTemperature_h
 
-#define DALLASTEMPLIBVERSION "4.0.1"
+#define DALLASTEMPLIBVERSION "4.0.2"
 
 // Configuration
 #ifndef REQUIRESNEW

diff --git a/library.json b/library.json
@@ -32,7 +32,7 @@
   {
     "paulstoffregen/OneWire": "^2.3.5"
   },
-  "version": "4.0.1",
+  "version": "4.0.2",
   "frameworks": "arduino",
   "platforms": "*"
 }
diff --git a/library.properties b/library.properties
@@ -1,5 +1,5 @@
 name=DallasTemperature
-version=4.0.1
+version=4.0.2
 author=Miles Burton <mail@milesburton.com>, Tim Newsome <nuisance@casualhacker.net>, Guil Barros <gfbarros@bappos.com>, Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Miles Burton <mail@milesburton.com>
 sentence=Arduino library for Dallas/Maxim temperature ICs