Patent GB-1475720-A (GB)
Title: Junction units
IPC: H04B3/00
Filed: 1974-12-19
Abstract: 1475720 Junction units WESTERN ELECTRIC CO Inc 19 Dec 1974 [21 Dec 1973] 55037/74 Heading H4P A junction unit for interconnecting a plurality of two way branch lines includes an incoming circuit and an outgoing circuit for each line and arrangements for establishing signal paths for data from the incoming circuit of any one line to the outgoing circuits of all other lines. If data is received concurrently by the incoming circuits of the one line and any other, the signal paths from the one line to the outgoing circuits of the remaining lines are disestablished, such that exclusive signal paths for data are established from the incoming circuits of the one and other lines to the outgoing circuits of the other and one line respectively. When only one branch is active, a gate matrix is instructed to broadcast the data received by the incoming circuit for the branch to all other branches and to pass an idle word to the outgoing circuit of the active branch. If a second branch becomes active, a control circuit recognizes this and delivers signals to interconnect the incoming circuit of each of the two active branches with the outgoing circuit of the other, a blocking signal is delivered to the input of the other remaining branches and an idle signal to their outputs. The other branches are then designated as inactive even should a signal appear. Finally, if all branches are idle, the idle word is applied to all outputs. More branches may be added. Data or "housekeeping" information reaches the junction unit in eight bit bytes on all branch input lines, e.g. (103(A), 104(A), 105(A) (Fig. 2). The eighth bit of a byte is a "1" or "0" depending on whether the byte is data or "housekeeping" (indicating that the branch is idle). The bytes on any one line, e.g. line 0, at 103(A) pass to a shift register, e.g. 222 and thence, via a cable 214, to a control circuit 301. The control circuit 301 incorporates a detector circuit, e.g. 312, and logic 312A for each branch. If the eighth bit of a byte is a "1", the flip-flop 319 is toggled by a byte clock pulse from the source 311 to deliver a "1" on its Q output. Provided two other lines, e.g. 1 and 2 are not already activated, which condition is detected by a gate 316 in logic circuit 312A so that a "0" at CP0 is sent to the gate 320, the Q output passes via the line 305 to pen a gate 223 and admit the byte to the gate matrix 212. A pulse on lead EI0 will be delivered when the two other branches are either both active or both inactive. In the matrix circuit 212, when CP0 is high, showing that the branch 0 is not excluded, pulses from one of the other two branches can pass via either gate 229 or 231 to the output line of branch 0. When only one branch is active a high signal from its CP control output opens the gates in the matrix so that its data is broacast to all other outputs. If EI0 is high, showing either that both other channels are idle or the 0 channel is excluded, idle words pass from the generator 303 via the gate 231 to the output circuit 209 of the branch 0. To modify the junction to allow for more branches, an additional detector and logic circuit must be provided in the control unit for each additional branch, and a gate circuit in the matrix. Each logic circuit must have additional gates so that it can examine the detector circuit outputs in pairs.