212 Rockwell Automation Publication 1766-UM001I-EN-P - June 2015
Appendix E Connecting to Networks via RS-232/RS-485 Interface
• maximum network segment of 1,219 m (4,000 ft.)
The DH-485 protocol supports two classes of devices: initiators and responders.
All initiators on the network get a chance to initiate message transfers. To
determine which initiator has the right to transmit, a token passing algorithm is
used.
Control of message transfers on the DH-485 network is performed by rotating
the token along the nodes on the network. A node holding the token can send a
message onto the network. Each node is allowed a fixed number of transmissions
(based on the Token Hold Factor) each time it receives the token. After a node
sends a message, it passes the token to the next device.
The allowable range of node addresses is 1…31. There must be at least one
initiator on the network (such as a MicroLogix controller, or an SLC 5/02 or
later processor).
DH-485 Configuration Parameters
When MicroLogix communications are configured for DH-485, the following
parameters can be changed:
See Software Considerations on page 215 for tips on setting the parameters listed
above.
Devices that use the DH-485 Network
In addition to the MicroLogix controllers, the devices shown in the following
table also support the DH-485 network .
DF1 Full-Duplex Configuration Parameters
Parameter Options
Baud Rate 9600, 19.2K
Node Address 1…31 decimal
Token Hold Factor 1…4
Devices that Support DH-45 Network
Catalog
Number
Description Installation Function Publication
Bulletin 1761
Controllers
MicroLogix 1000 Series C or later These controllers support DH-485 communications. 1761-UM003
Bulletin 1762 MicroLogix 1200 Series A or later These controllers support DH-485 communications. 1762-UM001
Bulletin 1763 MicroLogix 1100 Series A or later These controllers support DH-485 communications. 1763-UM001
Bulletin 1764 MicroLogix 1500 Series A or later These controllers support DH-485 communications. 1764-UM001
Bulletin 1747
Processors
SLC 500
Processors
SLC Chassis These processors support a variety of I/O requirements and functionality. 1747-UM011
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