H - Electricity – 04 – L
Patent
H - Electricity
04
L
340/74
H04L 7/00 (2006.01) H04J 3/06 (2006.01)
Patent
CA 1120120
D-21,803 FRAME SEARCH CONTROL FOR DIGITAL TRANSMISSION SYSTEM by Ralph LeRoy Kline ABSTRACT OF THE DISCLOSURE A frame search control circuit for a digital trans- mission system includes an eight bit preview store and a four stage counter. At the beginning of each frame a timing device causes the eight stored bits to be sequentially read out into a comparator for a comparison with bits from the incoming bit stream. The in- coming bits are stored in the preview store simultaneously with the read out to the comparator. For an in-frame condition only the first comparison is important and the remaining comparisons are ignored. Further, a count of eight is loaded into the four stage counter which limits the count to eight allowing only eight bits from the incoming bit stream to be read into the preview store, the framing bit being read in first so as to be available for comparison at the next framing interval. For an out-of-frame condition, the timing device initiates the sequential comparison beginning with the framing interval and in this case, each comparison is important. further, a count of eight is not loaded into the four stage counter. The counter begins counting from 1111 and, if a correct comparison occurs during any of the first eight counts, a load function is enabled. This causes a count of eight, 1000, to be immediately loaded into the counter. Also, for each count which is less than eight, a control signal is enabled which inhibits the framing clock for one time slot for each such count. Thus, the position of the frame interval is shifted so as to appear in the proper time slot D-21,803 once an in-frame condition is obtained. If a correct comparison is not obtained during the first eight counts, the control signal changes state allowing the framing clock to run and the next eight incoming bits are shifted into the preview store. In succeeding frames the process will be repeated until an in-frame condition is obtained.
340856
Gte Automatic Electric Laboratories Incorporated
R. William Wray & Associates
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