Rockwell-automation 1770-KF3 DH-485 Communication Interface User Manua User Manual download pdf (Page 34)

Chapter

41

Communicating with the KF3

Read this chapter if you are configuring a half-duplex network or if you

plan to write a communication driver. A thorough understanding of DF1

protocol, PLC command sets and the use of slave devices on the DH-485

communication network is required.

The KF3 supports full-duplex DF1 protocol and half-duplex DF1 slave

protocol on its RS-232C connection to a host computer. The details

of these protocols can be found in the Data Highway/Data Highway

Plus/DH-485 Protocol and Command Set Manual.

Full-duplex DF1 protocol is provided for applications where high

performance peer-to-peer communication is needed.

The KF3 provides two modes of addressing in half-duplex: local and

remote modes. You select one of these by configuring Submenu option 5 –

DF1 Device Category (see Table 3.C).

Local mode is provided for compatibility with earlier DF1 products,

such as the 1770-KF2. Some users may prefer local mode for use in

applications where the RS-232C link is not multidrop, since it simplifies

the polling algorithm.

Remote mode should be used with a half-duplex master, such as the

1771-KGM, or when SLC 500 communication is added to existing

half-duplex networks. Because the KF3 is transparent to the master

device, existing drivers can be used without rewriting.

FullDuplex DF1 Protocol

In full-duplex mode, the KF3 detects embedded responses. The module

will not send embedded responses until it receives one from the host.

The KF3 makes the assumption that if a host computer sends embedded

responses, it can also receive them.

In full-duplex mode, the destination address in a packet sent from the host

computer to the KF3 is the address of the DH-485 network node for which

the packet is intended. The source address in packets received by the host

computer from the KF3 is the node address of the sender.

DF1 Communication

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Rockwell-automation 1770-KF3 DH-485 Communication Interface User Manua User Manual Page 34