User guide

Communication Capabiliites
90
890 USE 108 00 August 2001
How the A984-
145, E984-245/
255/265/275/285
Initiates Modbus
Plus
Transactions
A984-145 (or any programmable controller with Modbus Plus capability) may initiate
network communication using a ladder logic function called MSTR. MSTR allows
you to specify the type of communications transaction you want to carry out and to
define the routing path over which you wish the transaction to take place.
The MSTR block is part of the standard A984-145, E984-245/255/265/275/285
instruction set, contained in the system executive. Modbus Plus transactions can be
accessed from the FFB communication library in the IEC program sections of
Concept for the E984-258/265/275/285.
How the A984-
145, E984-245/
255/265/275/285
Initiates Peer
Cop
Transactions
Point to point data can be transacted while a node holds the token and during its
token pass with Modbus Plus Peer Cop. Up to 500 words (16bits each) can be
directed to specific data references in node devices prior to release of the token
frame, and up to 32 words can be globally broadcast to all nodes as part of the token
frame.
Note: To have a good understanding of the Modbus Plus theory of operations, to
be able to plan the layout of the total network, and to meet all the requirements of
the network cable installation, refer to the Modicon Modbus Plus Network Planning
and Installation Guide (890 USE 100 00). Also, you may wish to refer to Modbus
Protocol Reference Guide (PI-MBUS-300). For a full description of the MSTR
function block, refer to the Modicon Ladder Logic Block Library User Guide (840
USE 101 00).
Note: In order to thoroughly understand Peer Cop theory of operations, to be able
to plan the layout of the total network, and to meet all the requirements of the
network cable installation, refer to the Modicon Modbus Plus Network Planning and
Installation Guide (890 USE 100 00).