Description
Model 485CON, RS-232 to RS-485 converter, converts unbalanced, full-duplex RS-232 signals to balanced, full-duplex or half-duplex RS-485 signals. RS-485 is an enhanced version of the RS-422 balanced line standard. It allows multiple drivers and receivers on a two-wire system.
The RS-232 port uses a male DB-25P type of connector with pins 2 (TD input) and 3 (RD output) supported. Protective Ground (pin 1) and Signal Ground (pin 7) are also connected. The RS-485 port uses a female DB-25S type of connector with Send Data outputs on pins 2 and 14, and Receive Data inputs on pins 5 and 17. Protective Ground (pin 1) and Signal Ground (pin 7) are connected through to the RS-232 connector.
The polarity of the two RS-485 lines must be correct. With no data being sent, the RS-232 line should be negative and the RS-485 "A" terminal should be negative with respect to the "B" terminal. If your equipment uses a " " and "-" naming scheme, in most cases the "A" line will be connected to the "-" and the "B" line will be connected to the " ". The RS-485 driver must be enabled when checking the polarity of the output of a RS-485 driver. On this connector, the RTS input (pin 4), on the RS-232 side must be raised to enable the RS-485 driver.
Figure 1 shows how to interconnect two RS-485 converters using two signal wires. The resistors Rt are optional, depending on the line length, baud rate, etc. The resistors should be about the impedance of the line used, which is normally about 120 Ohms each. Termination resistors are installed only at each end of the RS-485 multi-drop network. RTS must be off (low or marking) to receive and on (high or spacing) to transmit. Both RTS’s should not be on at the same time. Although you will not damage anything, the data sent will be garbled. If both RTS lines are off, the line may be floating and random data may appear on the outputs. Your protocol should allow for this if it can happen.
Up to 32 receivers can be driven by any one generator. This allows you to put together large systems with many drop points. The termination resistors should be located at approximately opposite ends of the system.
An external power supply is required (not included, sold separately).
