Single key subscriber connection with number of callers - has single key selection addresses ROM to provide coded output for serial transmission over standard lines

摘要

A telephone switching circuit enables a subscriber to make a number of predetermined calls by actuation of single push butons. A read-only-memory allows individual key signals to be converted into normal call coding, thus avoiding the need for more transmission lines. Typically a keyboard will have 256 keys, each key associated with a specified call location. The keyboard outputs are used to address a ROM, containing an 8 bit coding in two four bit groups. Output is entered into buffers and is multiplexed (JW) four bits at time. Timing signals for this process are provided by a clock circuit. A sender circuit transmits according to the coding standard adopted and a switching stage couples into the main transmission time.