QUESTION:
Is the 64k composite clock standard different in Japan than in the USA?
ANSWER:
The 64k composite clock standards are different in Japan than in the USA. They are, however, very similar. Both involve the transmission of a 64 kbps "all 1s" signal using, basically, alternate mark inversion (AMI). Therefore, there will be a pulse in each bit time, nominally of alternating polarity.
In the US standard the duty cycle is 5/8 whereas in Japan it is 4/8 (50%); also, the voltages are different, 6v-pp in the USA and 2v-pp in Japan. In both standards a byte boundary is indicated with a bipolar violation (BPV). That is, every eighth bit you will see a non-reversal of polarity (i.e. two pulses of the same polarity). The Japanese standard goes further, providing a 400 Hz "marker" which is indicated by a non-non-reversal (forgive the double negative) of a byte boundary. That is, every 20 octets the byte-boundary BPV is not introduced.
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