Aiming at the characteristics of the industrial control network

the paper studies a special MODEM

which can realize transparent transmission and direct parallel connection. A new method

256-decimal FSK

is used to modulate signals in the design. And within the transmission band of telephone line

an average transmission rate of 18.9 kbps can be obtained without data compaction. And there are no carrier waves without signal online. This paper presents the operating principle of multi-decimal FSK

system structure diagram based on MSP430F149 MCU and circuit of digital waveform generator. The waveform distortion generated in transmitting progress is analyzed and the solve method is put forward. Finally waveforms

in data transmitting experiments are provided.