POCSAG Basics

Introduction to POCSAG

POCSAG is a paging protocol that was developed by the British Post Office in the 1980s. This documentation does not attempt to explain the POCSAG protocol, only the LRS extensions to the protocol. For more information on POCSAG, please refer to the following websites:

• http://en.wikipedia.org/wiki/POCSAG
• http://www.aaroncake.net/schoolpage/pocsag.htm
• http://www.sxlist.com/techref/pager/pocsag.html

Character Encoding

The LRS implementation of POCSAG uses 7-bit ASCII character encoding. Furthermore, our implementation does not require an ETX or EOT at the end of the message. The remainder of the bits in the last codeword should be filled with zeroes (0).

Newline Encoding

Where line breaks are accepted, any of the following newline encodings are accepted by the alphapager:

• Unix / MacOS X style, ASCII LF (0x0A)
• DOS / Windows style, ASCII CR + LF (0x0D 0x0A)
• MacOS 9 and earlier style, ASCII CR (0x0D)

Function Code

POCSAG addresses pagers through capcodes. Capcodes consist of an 18-bit address and a 2-bit function code. All LRS alphapagers use a function code of 3. Normally this detail is handled by the transmitter.