thermocouple: Add initial support for common SPI temperature sensing chips

Signed-off-by: Petri Honkala <cruwaller@gmail.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

config/example-extras.cfg

@@ -631,6 +631,38 @@
 #   measurements must be provided.
 
 
+# MAXxxxxx serial peripheral interface (SPI) temperature based
+# sensors. The following parameters are available in heater sections
+# that use one of these sensor types.
+#[extruder]
+# See the "extruder" section in example.cfg for a description of
+# heater parameters. The parameters below describe sensor parameters.
+#sensor_type:
+#   One of "MAX6675", "MAX31855", "MAX31856", or "MAX31865".
+#spi_mode:
+#   The SPI mode to use when communicating with the chip. This
+#   parameter must be provided.
+#spi_speed:
+#   The SPI speed (in hz) to use when communicating with the chip.
+#   This parameter must be provided.
+#sensor_pin:
+#   The chip select line for the sensor chip. This parameter must be
+#   provided.
+#tc_type: K
+#tc_use_50Hz_filter: False
+#tc_averaging_count: 1
+#   The above parameters control the sensor parameters of MAX31856
+#   chips.  The defaults for each parameter are next to the parameter
+#   name in the above list.
+#rtd_nominal_r: 100
+#rtd_reference_r: 430
+#rtd_num_of_wires: 2
+#rtd_use_50Hz_filter: False
+#   The above parameters control the sensor parameters of MAX31865
+#   chips.  The defaults for each parameter are next to the parameter
+#   name in the above list.
+
+
 # G-Code macros (one may define any number of sections with a
 # "gcode_macro" prefix).
 #[gcode_macro my_cmd]