Publication 1785-UM012D-EN-P - July 2005
Communicating with Remote I/O 6-5
Cable Design Guidelines
Verify that your system’s design plans specify cable lengths within allowable
measurements.
For daisy chain configurations, use this table to determine the total cable
length you can use.
For proper operation, terminate both ends of a remote I/O link by using the
external resistors shipped with the programmable controller. Selecting either a
150Ω or 82Ω terminator determines how many devices you can connect on a
single remote I/O link.
TIP
Specify 1770-CD (Belden 9463) cable. Connect a remote
I/O network using a daisy chain or trunk line/drop line
configuration.
IMPORTANT
The maximum cable length for remote I/O depends on the
transmission rate. Configure all devices on a remote I/O
link to communicate at the same transmission rate.
Trunk line/drop line considerations:
When using a trunk line/drop line configuration,
use 1770-SC station connectors and follow
these cable-length guidelines:
trunk line-cable length*depends on the
communication rate of the link
drop-cable length*30.4 m (100 cable-ft)
For more information about designing trunk
line/drop line configurations, see the Data
Highway/Data Highway Plus/Data Highway
II/Data Highway-485 Cable Installation Manual,
publication 1770-6.2.2.
A Remote I/O Link Using
this Communication Rate
Cannot Exceed this
Cable Length
57.6 kbps 3,048 m (10,000 ft)
115.2 kbps 1,524 m (5,000 ft)
230.4 kbps 762 m (2,500 ft)
IMPORTANT
If you select the baud rate as 230.4 kbps, and you are using
the serial port or a PLC-5 coprocessor, use channel 2 for
better overall system performance.
If Your Remote I/O Link Use this Resistor
Rating
The Maximum number
of Physical Devices You
can Connect on the Link:
The Maximum
Number of Racks You
can Scan on the lLnk
operates at 230.4 kbps 82Ω 32 16
operates at 57.6 kbps or 115.2 kbps and no
devices listed in the following table are on
the link
contains any device listed in the following
table
150Ω 16 16
operates at 57.6 kbps or 115.2 kbps, and you
do not require the link to support more than
16 physical devices.
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