REMOTE CONTROLLED LINE CONCENTRATOR 



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3. The line selection circuit. 



4. The trunk identifier and selection relay circuits. 



(For an understanding of how these frame circuits work through the line 

 (link marker connector and markers in the No. 5 system, the reader 

 should consult the references.) 



The common central office circuits will be described first. 



a. Scanner Pulse Generator 



The scanner pulse generator, shown in Fig. 24, produces continuously 

 the combination of VG, VF and RS or reset pulses, described in connec- 

 tion with Fig. 18(a), required to drive the scanners for a number of 

 concentrators. The primary pulse source is a 1,000-cycle transistor 

 oscillator. This oscillator drives a transistor bi-stable circuit arranged 

 as a binary counter such that on each cycle of the oscillator output it 

 alternately assumes one of its states. Pulses produced by one state drive 

 a 5-stage counter. Pulses produced by the other state through gates 

 drive a 12-stage counter. 



The pulses which drive the 5-stage counter are the same pulses which 

 are used for the VF pulses to drive scanners. Each time the first stage 

 of the 5-stage counter is on, a gate is opened to allow a pulse to drive 

 the 12-stage counter. The pulses which drive the 12-stage counter are 

 also the pulses used as the VG pulses for driving the scanners. They 

 are out of phase with the VF pulses. 



When the last stage of the 12-stage counter is on, the gate which 



r VFC 



Fig. 24 — Scanner pulse generator. 



