FSK MODEM

摘要

A low-speed FSK data modem. A crystal-controlled oscillator drives a ripple-carry binary-counter. The intermediate outputs of the counter are selectively connected to four NAND-gates which decode the four counts which correspond to the four possible FSK output frequencies. Logic means are provided to ensure that the mark-to-space and space-to-mark transitions of the modem output are always graceful.