Rockwell Automation 1785-KA5P/B DHP COMM. ADAPATER MOD. - Manual (Page 10)

Overview of the 1785ĆKA5
Communication Adapter Module
Chapter 1
1-4
This section describes the DH485 network. For more information on this
network, see the DH/DH+/DH485 Protocol and Command Set reference
manual (publication 1770-6.5.16).
DH485 is a low cost, peer-to-peer programming and data acquisition link
for a variety of Allen-Bradley products, such as the SLC 500 family of
programmable controllers. A DH485 network provides a networking
solution for smaller applications (up to 32 nodes) within a small radius.
Each node has a unique station address between 0–31 decimal. The
maximum cable length is 4,000 feet. The DH485 link has a maximum
communication rate of 19,200 bits per second.
A DH485 network has a topology that is similar to that of a DH or DH+
network. DH485 is based on the EIA Standard RS-485 Electrical
Signalling Specification and implements token-passing protocol with
rotating mastership. The link protocol delimits messages, detects and
signals errors, retries after errors and controls message flow.
A variety of Allen-Bradley products, such as the SLC 500 family of
controllers, the SLC 500 APS programming software, the 1784-KTX,
-KTXD and -KR modules, and the 1770-KF3 module act as token-passing
masters on the DH485 network. The DH485 protocol also supports slave
(respond-only) mode for low-level devices on the network.
The 1784-KTX, -KTXD and -KR modules provide an IBM PC backplane
link to the DH485. It provides an asynchronous link to connect devices on
the network. An asynchronous device can interface with a DH485 module
directly or through a modem link.
The DH485 Network