Rockwell-automation 1770-KF2 Data Highway or Highway Plus Interface Mo Manual de usuario descargar pdf (Pagina 16)

Communication Concepts

Chapter 2

2-4

One station consists of an Advisor 2+

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.

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Rockwell-automation 1770-KF2 Data Highway or Highway Plus Interface Mo Manual de usuario Pagina 16