Patent GB-1205193-A (GB)
Title: Improvements to telegraph signal receiving systems
IPC: H04L12/52
Filed: 1969-03-19
Abstract: 1,205,193. Telegraphy. INTERNATIONAL STANDARD ELECTRIC CORP. 19 March, 1969 [28 March, 1968], No. 14393/69. Heading H4P. An arrangement for regenerating Start-Stop telegraph signals received on a number of groups grO-grm includes a unit BL which controls the scanning of the groups and, when a transition is detected, regenerates the appropriate bit of the character on the corresponding line. Certain of the circuits in BL are employed both during the transition detection operation and during the regeneration. The incoming lines are arranged in groups gr, each group containing lines of one speed and one code length only. It is arranged that scanner EX shall scan the groups containing the fastest lines first in each scan cycle. The number of groups scanned in a cycle varies, depending on the number of transitions detected, since the scan cycle has a fixed maximum duration. The parameters of the arrangement are such that all transitions in the lowest speed group are detected, although the group may not be scanned in each cycle. Assuming counter X to have been reset to zero a bi-stable MTT sets transition detector DT in operation. The state of counter X is read out to scanner EX, which selects the corresponding group of lines (grO in this case). The states of these lines are stored in BL, and a group word indicating the states of the lines at the previous sampling of group grO is read to BL from a group word store MGR. The group word also indicates the code length (e.g. 5-bit Start Stop) and speed of the signals in the line group. By comparison of the present and past states BL determines which lines, if any, of the group are in transition. If there is none, counter X is incremented and the next group grl is scanned. On the other hand if there is a line in transition, transition detector DT switches bi-stable MTT to start transition processor TT. Although DT and TT are shown separately most of the circuits used for transition detecting by DT are also used for processing by TT. Unit BL now reads from line store MLR that line word pertinent to one of the lines in transition in the group. The word has a section long enough to contain the longest code character and is up-dated by BL. Thus if the line word character read from MLR is 011000000 and a transition is detected at the sixth bit position the character is up-dated to 011001111, and read back to MLR. If other lines in the group are in transition, BL up-dates the relevant line words in the same way. When all the lines in transition in a group have been dealt with the counter X is incremented, MTT enables DT, and the next group is scanned. When a character has been completely reconstituted it is stored in an output queueing store for subsequent use. At regular periods, counter X is reset to zero. Any Start bit having less than ¢-bit duration is suppressed by determining the duration between an origin time, calculated with reference to the start of the'Start bit, and the time of the next transition. Also, by measuring the time of each transition relative to the origin time the distortion of each transition is determined. The line word records the maximum distortion.