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--- en:pfw:dht22-msp430g2553-noforth [2025-04-26 21:15] – mka
+++ en:pfw:dht22-msp430g2553-noforth [2025-06-26 12:41] (current) – [Sorce Code] mka
@@ Line 1: / Line 1: @@
+===== Read DHT22 data using noForth on TI's Launchpad.  (bit bang) =====
+[[en:pfw:dht22#implementation_for_ti_s_launchpad|go back]]
+==== Pseudocode ====
+<code>
+Function: Pio    ( -- )  \ set port I/O function. SDA --> P1.0
+Function: wakeup ( -- )  \ notify sensor to prepare the data
+Function: @data  ( -- sun moon hum tmp chk chksum )  \ get sensor data
+  get response time of sensor, store in register 'sun' (just for testing)
+  get startpulse duration, store in register 'moon'
+loop
+     read bit using 'moon' based delay
+     lshift bit into array xx yy zz
+loop
+     lshift array  \ adjust xx yy zz --> hum tmp chk
+  calculate chksum
+Function: (dht22)  ( -- sun moon hum tmp chk chksum ) \ wake up and read sensor
+Function:  dht22   ( -- )  \ print temperatur and humidity
+Function:  test    ( n -- ) \ multiple readings
+    n loop  dht22
+</code>
+==== Sorce Code ====
 <code>
 \ Read DHT22 data.  (bit bang)
@@ Line 199: / Line 224: @@
 ( finis)
 </code>
+==== Numerical representation of the measured values ====
+Note((This is already included in the source code.))
+=== Humidity ===
+The first 16 bits coming from the DHT22 are the relative humidity in tenths of a percent. They can be processed directly with the 16-bit noForth and correspond to a positive integer. Rounded to whole digits for display purposes.
+Here is an excerpt from the noforth source code:
+<code>
+: .hum ( hum -- )   10 / . ." %rel" space  ;
+</code>
+=== Temperature ===
+The next 16 bits are the temperature in tenths of a degree Celsius. Temperatures from zero degrees and higher can be processed directly using the 16-bit noForth; they correspond to a positive integer.
+Temperatures below zero degrees are represented by the DHT22 as follows: The MSB of the 16-bits is set, but otherwise the temperature is specified as a positive integer. This number format //does not correspond// to the two's complement of noForth. Here, the MSB must first be evaluated to determine the sign. The sign is prepended for output. The measured value can then be further processed as a positive integer.  Whole degrees are displayed to the left of the decimal point, tenths to the right. The unit °C is specified.
+<code>
+: .tmp ( tmp -- )
+  dup hx 8000 and hx 8000 =  \ check MSB
+      if [char] -
+      else [char] +
+      then emit
+  hx 7fff and ( tmp -- +tmp )    \ reset MSB
+/mod 3 .r [char] . emit .    \ --> TTT.T
+  [char] f decemit  [char] C emit  \ print °C
+  space
+  ;
+ </code>