Rockwell-automation 5730 DriveLogix5730 Controller for PowerFlex 700S Uživatelský manuál stáhnout pdf (Strana 182)

9-4 Communicating with Devices on a DH485 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.

If no network activity occurs, the initiator sends the token pass packet again.

After two retries (a total of three tries) the initiator attempts to find a new

successor.

Important: The maximum address that the initiator searches for before

starting again with zero is the value in the configurable parameter

“maximum node address.” The default value for this parameter is

31 for all initiators and responders.

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.

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Rockwell-automation 5730 DriveLogix5730 Controller for PowerFlex 700S Uživatelský manuál Strana 182