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The BLACK BOX Universal RS-232<ñ> RS-422/485 Converter with Opto-Isolation isolates and converts RS-232 signals into RS-422 / RS-485 signals and vice versa. Unlike other converters, external software is not required to control data flow. The RS-232 input is wired for DCE through a DB9 female connector, and RS-422 / RS-485 signals are interfaced through a removable terminal block.
For RS-232, the connection requires RD, TD, and signal ground. In RS-422 mode, the driver is always enabled for full-duplex communications. A twisted pair is required for transmit, and a twisted pair is also required for receive. A ground reference wire is also needed. In both RS-485 modes, the RS-485 driver is automatically enabled during each space state by the presence of an RS-232 signal. When the RS-232 data is in a mark or idle state, the RS-485 driver is disabled and the RS-485 data lines are held in a mark state by the bias provided by a 4.7-ohm resistor; the value of this resistor may need to be changed, depending on the termination you use. To connect to several RS-485 devices with minimal wire, select the unit's 2-wire, half-duplex RS-485 mode. When data is requested, the addressed device transmits and then reverts back to receive status.
For 4-wire master / slave circuits, select the unit's 4-wire, full-duplex RS-485 mode. In this mode, addressed devices can receive data while transmitting data from a previous request. When used as a master in a single-master system, Switch 1 may be selected because the unit is the only transmitter in the system. When used as an RS-485 slave, the RS-232 device must provide addressability. Biasing in a master / slave system is provided by the end-of-line slave.