Rockwell Automation 5720 DriveLogix System - Manual (Page 214)

Publication 20D-UM002C-EN-P - November 2003
10-4 Communicating with Devices on a DH-485 Link
Specify these characteristics on the Serial Port tab (default values are shown in
bold):
Planning a DH-485 Network The DH-485 network offers:
• interconnection of 32 devices
• multi-master capability
• token passing access control
• the ability to add or remove nodes without disrupting the network
• maximum network length of 1219 m (4000 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. The DH-485 protocol uses a token-pass algorithm to determine
which initiator has the right to transmit
DH-485 token rotation
A node holding the token can send any valid packet onto the network. Each
node gets only one transmission (plus two retries) each time it receives the
token. After a node sends one message packet, it attempts to give the token to
its successor by sending a “token pass” packet to its successor.
Characteristic: Description (default is shown in bold):
Baud Rate Specifies the communication rate for the DH-485 port. All devices on the same DH-485
network must be configured for the same baud rate. Select 9600 or 19200 Kbps.
Node Address Specifies the node address of the DriveLogix controller on the DH-485 network. Select a
number 1-31 decimal, inclusive.
To optimize network performance, assign node addresses in sequential order. Initiators,
such as personal computers, should be assigned the lowest address numbers to minimize
the time required to initialize the network.
Token Hold Factor Number of transmissions (plus retries) that a node holding a token can send onto the data
link each time that it receives the token. Enter a value between 1-4. The default is 1.
Maximum Node
Address Specifies the maximum node address of all the devices on the DH-485 network. Select a
number 1-31 decimal, inclusive.
To optimize network performance, make sure:
• the maximum node address is the highest node number being used on the network
• that all the devices on the same DH-485 network have the same selection for the
maximum node address.