Patent GB-1340078-A (GB)
Title: Code conversion of electrical signals
IPC: H03M7/04
Filed: 1970-12-23
Abstract: 1340078 Code conversion WESTERN ELECTRIC CO Inc 23 Dec 1970 [23 Dec 1969] 61071/70 Heading G4A A data processing system converts digital signals coded in a 2 out of n constant duty code into equivalent binary coded signals by generating binary signals indicative of the position of the 2 "one" bits relative to a fixed one of the n bits, shifting a fixed binary pattern by a number of places equal to the value of one of the position signals above and adding together the two position indicating signals above and a part of the shifted pattern to produce the binary coded equivalent of the 2 out of n code. Special purpose circuit.-A clock pulse train is connected to input 102 and the divider 109 generates an output on the occurrence of every 7th clock pulse which gates a new 2 out-of-6 code into shift register 101, blocks the gate 103, resets the counter 111 and shift register 112, gates the result of the previous decoding to the output, and, via a short delay, resets the accumulator register 115. The next six clock pulses pass through a gate 103 and shift the 2 out-of-6 code out of register 101. When the first "one" bit reaches the output stage it gates the contents of counter 111, initially all "ones" which have been counted down by the clock pulses, into the accumulator 115. When the second "one" bit reaches the output of register 101 the contents of counter 111 are again gated to the accumulator where they are added to the previously gated contents of the counter. The second "one" bit in register 101, via divider 106 and delay (to allow the accumulator to settle), also gates the four most significant bits from shift register 112 into the accumulator 115. The register 112 is initially loaded with a pattern, viz "one" in the two least significant places and "zero" in the remaining places, which remains fixed but is rotated one place by each clock pulse on line 113. The contents of the accumulator are then gated out, and subsequently cleared by the seventh clock pulse which sets the next 2 out-of-6 code in the register 101. General purpose computer.-In addition to the special purpose circuit above the specification also gives (in full) a computer program by means of which the conversion can be made. The computer may control an electronic telephone exchange in which 2 out-of-6 coded dialling signals are converted into simple binary for processing and may be similar to that described in Specification 1,260,090. The conversion program is in the form of a subroutine called by means of a transfer instruction. The main program instructions are normally called by incrementing the contents of an instruction register. A masking circuit is described which allow operations, e.g. logic functions or data transfer &c. to be performed only on bits for which the corresponding bit in the mask register is a "one". A sum-rotate register is provided for rotating a bit pattern or for rotating the contents of one register and adding them to those of a second register. Error indications are provided if the incoming code contains other than 2 "one" bits out of 6.