
!"##$%&'()&%*+,-."$*-+)-/
7"8$9/
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5–2
The computer is attached to the Data Highway Plus via the RS-232-C
connection to the 1785-KE. In this configuration, the computer assumes
the address of the 1785-KE on the Data Highway Plus, i.e., the computer
and 1785-KE are addressed as a single node on the Data Highway Plus. As
a result, messages sent from other nodes on the Data Highway Plus to the
computer will use the address of the 1785-KE as the destination address.
Messages sent from the computer to other nodes on the Data Highway Plus
will use the address of the 1785-KE as the source node address.
The following example will use the system of figure
5.1
to illustrate
commands initiated by the computer to PLC-5 051. The full duplex
protocol is used in the examples.
You may wish to refer to Appendix D, “Interprocessor Addressing”, for
further background information on communicating from a computer to a
PLC-5.
!*+$,%&'(%*(AI!5)
In this example, we show the computer sending the following commands
to the PLC-5:
PLC-2 read and write commands
PLC-3 read and write commands
We display the command formats that are sent over the RS-232-C link as
they would appear on a line monitor placed between the computer and its
1785-KE Data Highway Plus module (all line monitor printouts are shown
in hex). Full-duplex protocol is used.
In this example:
computer (1785-KE) node address 040 (octal) = 020 (hex)
PLC-5 node address: 051 (octal) = 029 (hex)
Important:
If the computer sends a PLC-2 type command to the PLC-5,
then the PLC-5 must create a PLC-2 compatibility file number 32
[computer node address 040 (octal) = 032 (decimal)]. This file must look
like a PLC-2 data table to the computer.
If the computer sends a PLC-3 type command with a four-level extended
address to the PLC-5, the command will be able to access any file in the
PLC-5 data table.