Installation
21
User’s Manual - SM19202 Fast Poll Modem
S3-3 RS-485 Receiver Termination
When RS-485 is used, a 120 ohm receiver termination may be used to terminate the
receiver.
•
S3-3 ON,
a 120 ohms load is placed across the RX+ and RX- signal
•
S3-3: OFF, no termination is connected to the receiver
S3-4-
Not Used
S-3-5
Leased Line Receiver Termination
S3-5 ON: The modem leased line receiver is terminated with 600 ohms (default)
S3-5 OFF: The modem’s line receiver is set high input impedance (multi-point)
S3-6-
Common Signal Ground and Chassis Ground
S3-6 ON: The modem chassis ground and signal ground are connected
S3-6 OFF: The modem chassis ground and signal ground are not connected.
Configuring the Jumper Blocks
For Stand-alone Units
No internal jumper block is required.
For Rack-Mount Plug-in Modules
Jumper block JP1 is used to set the modem’s receiver termination impedance
•
600 ohms: A shorting jumper is placed over pin 2 & 3 (default)
•
High impedance: A shorting jumper is placed over pin 1 & 2
Select high receiver impedance (Hi-Z) if multiple modems are connected in a multi-
point configuration but without an impedance matching bridged such as private
metallic circuit environment. In this configuration, only one receiver should be
configured for 600 ohms.
