CMI code has certain advantages such as smaller low-frequency components , easier to extract signals from the clock, and the ability to seize wrong. So according to CCITT recommendations, CMI code generally use as four groups PCM digital interface code relay Type in the number of program-controlled switches. The article through analyzing the principle of CMI codec, expertize a programmable logic device based on the realization of the CMI encoding and decoding methods, giving the hardware design schematics, software design processes and the CMI codes simulation waveform. This method has the advantages of simple hardware design, fast running and low cost . At the same time as CPLD has the characteristics of repeating programming , it can carry out on-line changes ,convenient to the commissioning and operation of equipment. Keywords: CMI code, CPLD, VHDL language
