4. A control word source of claim 3 wherein said frame signal generator means comprises frequency divider means responsive to said timing pulses for generating frame pulses at a rate of one frame pulse per fixed number of said timing pulses and counter means responsive to the frame pulses generated by said frequency divider means for generating said frame signals by counting said generated frame pulses.
4. A control word source of claim 3 wherein said frame signal generator means comprises frequency divider means responsive to said timing pulses for generating frame pulses at a rate of one frame pulse per fixed number of said timing pulses and counter means responsive to the frame pulses generated by said frequency divider means for generating said frame signals by counting said generated frame pulses. 6. A control word source of claim 4 wherein said counter means comprises a plurality of modulo counters each responsive to said generated frame pulses for generating a unique repeating sequence of frame signals.