| 摘要 |
Each decoder has a random access memory storing program code numbers, a security number, a customer identification number, and program identification numbers utilized for billing purposes. Communication between each decoder and a central computer is subscriber-initiated. The program code numbers must be updated periodically by means of a computer-decoder transmission which takes place only after the program identification numbers have been transmitted from the decoder to the computer. During predetermined cycles in the system sequence, the read-out of the random access memory takes place in reverse order and starting at an arbitrary start point hard-wired into each decoder. Confusion signals are transmitted while program identification numbers already transmitted to the computer are erased in the decoder memory. The communication through the telephone network takes place by frequency shift keying.
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