Watlow MICRODIN - Manual (Page 14)

2 . 4 Wa t l o w M i c r o D I N
Special Case 485 Network Considerations
If your EIA-485 network does not work, it may require termination resistors.
Termination Resistor at the Last MicroDIN
In some cases long distance networks may require termination resistors. If the
continuity checks good and you still cannot get valid responses, add termination.
You can make a terminator by placing a 120½ resistor across the C and D
terminals of a standard RJ-11 phone plug. Plug the terminator into the open
socket in the furthest MicroDIN from the computer.
See Chapter 3 , ÒInstallation and Wiring,Ó for a wiring diagram.
Termination and Pull-Up/Pull-Down Resistors at the Converter
If you use a terminator, you should also add pull-up and pull-down resistors to
the EIA-485 converter box.
Place a 120-ohm resistor across the transmit/receive terminals (C and D) of the
converter box.
Add 1K½ pull-up and pull-down resistors as shown in Chapter 3 to maintain the
correct voltage during the idle state.
See Chapter 3 for wiring diagram.
Communication
Setup
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CAUTION:
Apply termination and
pull-up/pull-down
resistors only if
necessary to establish
data communications.
Adding this resistance to
a network where it is not
required could result in
loss of communications
and damage to process
product.