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THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 195(5 



transmits pulses to the 12-stage counter is closed and another gate is 

 opened which produces the reset pulse. The reset pulse is thereby trans- 

 mitted to the scanners in place of the first vertical group pulse. At the 

 same time the 5 and 12-stage counters in the scanner pulse generator 

 are reset to enable the starting of a new cycle. 



In the central office control circuits, out of phase pulses on lead TP 

 similar to those which drive the VG counters at the concentrator are 

 used for various gating operations. 



b. The Originating Call Detection and Line Number Registration 



The originating call detector (Fig. 25) and the originating line num- 

 ber register (Fig. 26) together receive the information from the line 

 concentrator used to identify the number of the line making a service i 

 request. The receipt of the service request pulse from a concentrator i 

 in a particular time slot will set a transistor bi-stable circuit HGT of { 

 Fig. 25 associated with that concentrator if no other originating call is 

 being served by the frame circuits at* this time. 



The originating line number register consists of a 5 and 12-stage 

 counter. These counters are normally driven through gates in syn- 

 chronism with the scanning counters at concentrators with pulses sup- 

 plied from the scanner pulse generator. When a service request pulse 

 is received from any of the concentrators served by a line link frame, a 

 pulse is sent to the originating line number register which operates a 

 bi-stable circuit over a lead RH in Fig. 26. This bi-stable circuit then 

 closes the gates through which the 5- and 12-stage counters are being 

 driven, and also closes a gate which prevents them from being reset. 



TO TRAFFIC I 

 RECORDER I 



TO ORIGINATING 

 CALL REGISTER 



I TO CONCENTRATOR 

 I CONTROL TRUNK 



Fig. 25 — Originating call detector. 



