Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 11)

Introduction
Chapter 1
1-7
In either type of configuration, there are three possible ways you can
connect a KF2 module:
Direct connection to an intelligent asynchronous device if the KF2
module is mounted within 50 cable-feet of an RS-232-C, or within
4,000 cable-feet of an RS-422-A device.
Direct connection to an Allen-Bradley 1775-KA, 1773-KA, or
1771-KG interface module if the KF2 module is within 50 cable-feet of
the other module.
Modem connection if the KF2 module is within 50 cable-feet of an
RS-232-C compatible modem, or within 4,000 cable-feet of an
RS-422-A device.
You can also use the 1770-KF2 module to replace a 1771-KD module in
an existing application. By properly setting the option switches on the
KF2 module, you can make this replacement without having to change
any application programs that you were using with the 1771-KD module.
Refer to Chapter 3 under “Replacing a 1771-KD Module with a KF2
Module” for switch settings.
A 1770-KF2 Series B module provides either a point-to-point or
multi-drop link between an Allen-Bradley Peer Communication Link
(PCL) and an intelligent asynchronous device. You can use a PCL link
when you have a small number of PLC-5/15 stations in a local cluster.
Typically, a PCL link connects PLC-5/15s that need to communicate with
each other frequently. If your system requires more than ten stations,
consider breaking it into smaller PCL links connected by a Data Highway
to optimize performance.
The KF2 Series B module provides an interface between either:
an RS-232-C or RS-422-A asynchronous link to Data Highway, or
an RS-232-C or RS-422-A asynchronous link to a PCL network as
shown in Figure 1.4.
PCL Applications