Research And Implementation Of Nonpolar RS485 Interface Chip

With the advantages of simple in design, convenient in controll and low cost, RS485 bus has became first choise among long distance data transmission fields such as intelligent electric network. In domestic market, RS485 is widely used in industrial control, electric communication, intelligent house, instrument, multi-media network, mechanotronics, supervisory control system, etc. Owe to technology limitation, one main problem exits during application, which is traditional RS485 interface must not connect communication port A or B to the wrong polarity, or it may lead to failure. In order to prevent that potential problem, it has great academic and ecnomical meaning to realize an RS485 interface chip with non-polarity feature.Based on universal RS485 communication standard, this dissertation designed a non-polarity RS485 chip by using MXIC 0.5um high voltage process and Cadence EDA tools. Sub-blocks like transmitter, receiver and non-polarity controller has been carefully designed and layouted. The chip has been taped out and tested, the main work and contributions of this dissertation are as followings:1. In transmitter design, forward 3 methods were brought to interact so as to control the slew rate appropriately.2. In transmitter’s output circuit design, output mosfets were used as ESD conponents at the same time, thus chip area was saved.3. Low power control circuit was designed in order to shut down the whole chip while enable signals in transmitter and receiver were not effective. In non-polarity function design, by control oscillator output cycle and number of frequency divider, polarity judgement and time to change polarity were determined.In addition to basic specifications while transmitting and receiving data, this dissertation emphasized on realizing non-polarity feature via adding polarity control and judgement circuit.