Allen-Bradley 1779-KFMR User Manual page 15

Chapter 2
Introducing the 1779 KFM Interface
2 8
Programming
The program in a host device at one node can initiate a transfer of a
message to or from any other node in the network. Programming a host
computer for communication through a 1779-KFM interface is described
in later chapters.
Host/Interface Links
In many applications, it is essential for nodes in a Data Highway II link to
communicate with devices such as:
Computers
Color-Graphic Terminals
Dumb Terminals
Robots
Computerized Numerical Controls (CNC)
For this type of device to communicate with nodes in a Data Highway II
link, it must communicate through a local host/interface link and a node
interface to the Data Highway II link (Figure 2.5).
Figure 2.5 shows three such devices, each communicating through a local
host/interface link and a node interface to a Data Highway II link.
A computer is shown communicating with other nodes of the Data
Highway II link through an RS-422/449 link and a 1779-KFM
interface. A 1779-KFM interface has a single RS-422/449 channel
through which it can interface an RS-422/449 compatible device to the
Data Highway II link.
An 8200 CNC is shown communicating with other nodes of the Data
Highway II link through its Factory Communication Module
(Cat. No. 8200-KDHW), an RS-422 link, and a 1779-KFL interface.
A dumb terminal is shown communicating through an RS-232-C link
and a 1779-KFL interface with other nodes of the Data Highway II
link. Each 1779-KFL interface has two channels for connection to two
host devices at the same time. Through either channel it can interface
either an RS-232-C compatible device or an RS-422 compatible device
to the Data Highway II link.
You can use a host device to communicate through either an RS-422/449
link to a 1779-KFM interface or an RS-232-C or RS-422 link to a
1779-KFL interface in a packet assembler/disassembler (PAD) protocol.
The PAD protocol is useful for communicating with robots and dumb
terminals.