Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 16)

Communication Concepts
Chapter 2
2-4
One station consists of an Advisor 2+ TM Color Graphic System connected
to a KF2 module through an RS-232-C link limited to 50 cable-feet.
Another station consists of a computer interfacing with a KF2 module
through a modem link that is limited only by the nature of the modems
themselves.
The third such station consists of a 1771-KG module interfacing a
PLC-2/30 processor with a KF2 module through an RS-232-C link limited
to 50 cable-feet. If you want a link longer than 50 cable-feet, you can use
modems.
PC Programming
All Allen-Bradley PC processors can be connected to a Data Highway
through an appropriate station interface module. All of these processors
can receive and reply to command messages, and some of them can also
transmit command messages. For an explanation of how to program PCs
to send and receive messages, refer to the user’s manual for the
appropriate station interface module.
Computer Programming
The communication protocol for the Data Highway link is transparent to a
computer on the network. However, for a computer to send or receive
messages through the Data Highway network, it must be programmed to
communicate with its KF2 module over an asynchronous link.
Chapters 4, 5, and 6 describe the protocol that you must program your
computer to use on such an asynchronous link.
Peer Communication Link
A PCL has much the same topology as the Data Highway, described in the
previous chapter; but it is designed for fewer, closely coupled, PCs. The
PCL implements peer-to-peer communication with a token-passing
scheme to rotate link mastership among the stations connected to that link.
Since such a method does not require any polling, it is very time efficient.
The PCL also uses timeouts to recover from any fault that disables the
station that has the token.