Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Bedienungsanleitung PDF herunterladen (Seite 223)

13–8 PLC Addressing

Publication

17706.5.16 - October 1996

PLC3 Symbolic Addressing

Symbolic addressing uses ASCII symbols to represent a logical

address. Before using a symbolic address in a message, you must

first define the symbol at the PLC-3 processor that is to receive the

message. (For more information, refer to your PLC-3 user manual.)

The symbolic address field can be from 1 to 8 bytes long:

• The first byte contains the ASCII code for the first character in

the symbol name

• The second byte contains the ASCII code for the second character

• and so on

If the symbol name is more than 8 characters long, encode only the

first 8 characters.

This module Accepts

1775KA ASCII symbols

1775S5, SR5

•ASCII symbols

•logical ASCII

All revision levels of 1775S5, SR5 accept PLC5 type reads and type

writes. 1775S5, SR5 series A, revision E or later can also use logical

ASCII with a PLC3 word range read or word range write.

Example of logical ASCII:

hex bytehex

byte

ASCI

00 $N0:0 00

To use a symbolic address in a command message, encode the

symbol in the field labelled ASCII symbol in the command message

formats. (See Chapter 7, “Communication Commands.”)

The message formats show a byte of value zero before and after the

symbolic address field. You must include these zero bytes because

they act as delimiters to distinguish the symbolic address from other

fields in the message

Important: Only PLC-3 controllers can transmit commands that

contain symbolic addresses. If you plan to transmit this

type of command message to your computer from a

PLC-3 node, you must write computer application

programs that are capable of accepting these commands

and interpreting the symbolic addresses.

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Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Bedienungsanleitung Seite 223