CHAPTER 4: Option Selection
Signal | | Name | Pin # | Mode |
GND | | Ground | 7 | |
TDB | TX+ | Transmit Positive | 24 | Output RS-422 |
TDA | TX- | Transmit Negative | 25 | Output RS-422 |
RDB | RX+ | Receive Positive | 12 | Input RS-422 |
RDA | RX- | Receive Negative | 13 | Input RS-422 |
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RS-530/422/485 Line Termination
Typically, each end of the RS-530/422/485 bus must have line-terminating resistors. A 100-ohm resistor is across each RS-530/422/485 input, in addition to a 1K ohm pull-up/pull-down combination that biases the receiver inputs. DIP switch SW2 allows you to customize this interface to your specific requirements. Each switch corresponds to a specific portion of the interface. If multiple RS422/485 Serial Interface Plus adapters are configured in a network, only the boards on each end should have switches 1, 2, and 3 ON. Refer to the following table for each switch’s operation:
Name | Function |
T | Adds or removes the 100-ohm termination. Switch 1 ON adds the |
| termination, and OFF removes the termination. |
| |
P | Adds or removes the 1K ohm pull-up resistor in the RS-422/RS-485 |
| receiver circuit (Receive data only). Switch 2 ON adds the 1K pull-up |
| resistor and OFF removes the pull-up resistor. |
P | Adds or removes the 1K ohm pull-down resistor in the RS-422/RS-485 |
| receiver circuit (Receive data only). Switch 3 ON adds the 1K pull-down |
| resistor, and OFF removes the pull-down resistor. |
| |
L | Connects the TX+ to RX+ for RS-485 two-wire operation. |
| |
L | Connects the TX- to RX- for RS-485 two-wire operation. |
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