Rockwell Automation 1747-DSN DISTRIBUTED I/O SCANNER - Manual (Page 16)

Chapter 2
Wiring and Installation
2–4
The DH–485 Data Link allows a programming device to communicate with
the SLC processor. Each I/O block has a programming port that allows a
programming device to be connected to the DH–485 Data Link.
The Isolated Coupler and I/O blocks are connected to the DH–485 Data Link
in a daisy chain configuration. A daisy chain configuration is formed by
connecting the Isolated Coupler and I/O blocks together in a serial manner
along a single section of link cable (Belden 9842).
There are no restrictions governing the spacing between each device, as long
as the overall length of the DH–485 Data Link does not exceed 4,000 feet.
However, no two devices may be connected to the same point on the
DH–485 Data Link. Termination must be provided at each end of the link.
The I/O blocks and Isolated Couplers have internal resistors for this purpose.
Incorrect
Correct
Last device must
be terminated
Incorrect
Correct
Isolated Link
Coupler
Last device must
be terminated
Last device must be
terminated
Last device must
be terminated
Last device must be
terminated
Last device must be
terminated
1747–C11
Communication
Cable
Programming
Device (APS)
Programming
Device (HHT)
Belden 9842
Last device
terminated
1747–C10
Communication
Cable
Last device
terminated
Important: The device at each end of the link must be terminated using the
DH–485 Termination Switch (switch 10).
Wiring the DH–485 Data
Link