These are my general notes on a type of decoder I have used on several projects to decode serial message inputs.

 The input is a series of digital pulses that represent words of a serial message. The message should have a distinctive preample word to identify as as a message, the type of message and the start of message.
The preamble word is followed by further words that make up the rest of the message.
 The preamble as the start of message is usually detected in the leading edge of the pulse. After detecting the preamble the rest of the message can be clocked into the circuit in the centre of the other pulses as shown in the following diagram.
The word can be clocked into the circuit at the center of the word. The message controller comprises a delay line to enable the preamble of the message to be decoded in a parallel by a preamble decoder. The timig circuit can be reset during the low (0V) of the pulse to avoid any spikes.