| 摘要 |
PURPOSE:To secure detection of an FS(frequency shift) signal and also to miniaturize a unit by detecting a frequency on the basis of a count value in the half-cycle period of FS by a modem. CONSTITUTION:A received FS signal is made into pulses at WF and at its rise, FF1 is set to make counter CT1 count clock CLK with the Q output of FF1. On the end of a frequency period when respective bits of the FS signal are expressed, pulse (c) is supplied to counter CT2 and after one word of the FS signal is counted, output (d) is obtained to set FF2, output (e) of which is supplied to a data identifying circuit as signal END indicating the end of FS signal reception. Further, differentiation DF of signal (a) made into pulses is carried out, and bits for one word are supplied to shift register SR with its output. Further, counter CT3 counts CLK in the half-cycle period of a low frequency to obtain output DL. On the basis of outputs of signals END, DL and SR, the data identifying circuit detects the FS signal. |
