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DF1 Communication
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.
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