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What's required for a Short Range Multipoint Modem to operate Two Wire?
Posted by Bob Puckett, Last modified by Danny Staub on 15 November 2017 03:44 PM
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First of all, the communication equipment must control Request To Send (RTS). This is very important, when a modem detects an ON (+ voltage) on Pin 4 (RTS) it switches the transmitter from High Impedance to Low Impedance. If two or more pieces of equipment have RTS - ON, the line will be clamped and there will be no transmission possible. These modems operate in Half-Duplex only when they are configured for Multi-Point operation. For Half-Duplex operation all equipment must have RTS-OFF, a negative voltage on Pin 4 of the RS-232/V.24 serial port. Typical Half Duplex communications will function as follows:
A Master unit will Poll with addresses of slave units. The Master unit turns ON RTS sends the address of a slave unit, turn RTS OFF. The Slave unit receives it's address, turns ON RTS sends the information then turns OFF RTS. | |
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