OPTO 22 SNAP-PAC-R1, Руководство пользователя

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CHAPTER 3: SYSTEM INFORMATION
SNAP PAC R-Series Controller User’s Guide
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Using Data for Peer-to-Peer Communication
What if you have multiple SNAP PAC controllers? What if each one is running a different PAC
Control strategy, and they need to share variable data? Or what if you need to share data
between a SNAP PAC System and an Allen-Bradley Logix-based PLC?
Scratch Pad areas within the SNAP PAC R-series controller’s memory map provide a way for
other devices on the Ethernet network to access data in the controller. For descriptions of
the Scratch Pad areas—bits, integers, floats, and strings—see the
PAC Manager User’s Guide .
For help in using PAC Control commands to access Scratch Pad areas, see “I/O
Unit—Scratch Pad Commands” in Chapter 10 of the
PAC Control User’s Guide . For
information on communicating with an A-B Logix PLC, see the EtherNet/IP for SNAP PAC
Protocol Guide .
The following illustration shows how this type of peer-to-peer communication can be done
using PAC Control.
The memory map in the
controller’s I/O side has
two parts: the fixed area
and the Scratch Pad area.
The fixed memory area is
used automatically by the
controller to read and
write data to I/O points;
each address has a fixed
purpose.
The Scratch Pad area,
however, is user-defined; it
is available for you to
define and use as needed
in order to exchange data
among peers.
The Scratch Pad area
includes five sections so
you can use different types
of data: bits, 32-bit and
64-bit integers, floats, and
strings.
Using PAC Control
commands in its flowcharts, the first SNAP PAC R-series controller can write strategy variable
data to its Scratch Pad area. Other SNAP PAC controllers can use similar commands in their
own flowcharts to read the data from the Scratch Pad area of the first controller. Similarly,
another unit or controller can write to the Scratch Pad area of the first controller, which can
then read the data deposited in its own Scratch Pad area by the peer. The reading and
writing of data by peers to the Scratch Pad area must be very carefully coordinated in order
to avoid conflicts.
SNAP PAC R-series
I/O Unit
Control Side
Run PAC Control flowcharts
I/O Side
Read/write to points
using Memory Map
Shared tag
database
Fixed memory area
(I/O point data)
Scratch pad area
(strategy variable data)