Fix data pos overflow

README.md

@@ -1,17 +1,33 @@
-dcf77
-======
-
-_dcf77_ contains a state machine to identify a [DCF77][] signal fed in to a
-regular GPIO pin. It also contains a decoder for the received signal into
-date/time values.
-
-The driver is hardware independent and can e.g. be used with microcontrollers and
-any implementation of an [embedded-hal][] crate.
-
-[embedded-hal]: https://github.com/japaric/embedded-hal.git
-[DCF77]: https://en.wikipedia.org/wiki/DCF77
-
-License
--------
-
-[0-clause BSD license](LICENSE-0BSD.txt).
+dcf77
+======
+
+_dcf77_ contains a state machine to identify a [DCF77][] signal fed in to a
+regular GPIO pin. It also contains a decoder for the received signal into
+date/time values.
+
+The driver is hardware independent and can e.g. be used with microcontrollers and
+any implementation of an [embedded-hal][] crate.
+
+The input signal of the dcf77 statemachine shall look like this
+
+```text
+DCF77 RF signal:
+
+   |     |||||||||||||||||||||||||||||||||||||        |||||||||||||||||||||||||||||||    |||
+   |     |||||||||||||||||||||||||||||||||||||        |||||||||||||||||||||||||||||||    |||
+   |     |||||||||||||||||||||||||||||||||||||        |||||||||||||||||||||||||||||||    |||
+...|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||...
+
+DCF77 receiver output that can be fed into this state machine:
+     ___                                      _______                                ___
+..._|   |____________________________________|       |______________________________|   |___...
+    100ms               900ms                  200ms              800ms             100ms      
+```
+
+[embedded-hal]: https://github.com/japaric/embedded-hal.git
+[DCF77]: https://en.wikipedia.org/wiki/DCF77
+
+License
+-------
+
+[0-clause BSD license](LICENSE-0BSD.txt).