Point-to-Point
When only two devices are connected to the line in a point-to-point application, each device should have the termination network connected to the line. Set switch S2 to the “TERM” position.
Multipoint
For multipoint applications, switch S2 should be in the “UNTERM” position on all the RS-232↔485/422 Converter devices in the network except for the two units at the extreme opposite locations on the line. The extreme opposite devices are the two devices that have the greatest cable length between them, which may not necessarily be the devices that are physically located the farthest apart. These two units should be set in the “TERM” position (see Figures 5 and 6). If any of the other RS-232↔485/ 422 Converters were configured as “terminated,” the amount of distortion could increase—possibly causing errors in the data being transmitted.
3.1.8NORMAL/LOOPBACK OPERATION
The Normal/Loopback switch (S1) is a two-position pushbutton switch extending through the front panel. The Normal position permits normal operation of the RS-232↔485/422 Converter. The Loopback position allows data coming into the RS-232↔485/422 Converter to be sent back out the same port. This is for testing the connection between the RS-232↔485/422 Converter and the device attached to each port.
Normal
When this switch is in the normal mode, data is passed through the Converter from the RS-232 port to the RS-485 port and vice versa.
Loopback
When set to the loopback mode, any data received at the RS-485 port will be transmitted back out the RS-485 port and any data received at the RS-232 port will be transmitted back out the RS-232 port.
3.1.9RS-485 INTERFACE LINE BIASED (FAIL-SAFE)
If S3 is in the Off position, there is no line bias. If S3 is in the On position, there is line bias.
