Message compression encoder and encoding method for a communication

Abstract

A message compression encoder for a communication channel carrying messages onstructed of characters from a predetermined character set includes a read-only memory (ROM) and input and output temporary storage buffers respectively connected to input address ports and output data ports of the memory. The ROM has storage locations storing comma-free code words representing characters of the character set in accordance with predetermined probabilities of occurrence in messages carried by the communication channel. The input buffer receives fixed-length code words representing characters of messages carried by the communication channel and arranges them to generate addresses of the ROM storage locations for addressing the same. The ROM is operable in response to addressing of its storage locations to output stored fixed-length comma-free code words. These stored code words contain variable-length code words representing the same characters represented by the fixed-length code words but are composed of fewer bits than compose the fixed-length code words. The output buffer receives the stored code words from the ROM and a detector connected to the output buffer separates and outputs the variable-length code words. The ROM also is operable upon addressing of a predetermined code word stored therein of outputting such code word to the input buffer to cause resetting of the buffer.