CHAPTER 3: SYSTEM INFORMATION
SNAP PAC R-Series Controller User’s Guide
19
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.
For more information on using PAC Control commands for peer-to-peer communication, see “Communication
Commands” in Chapter 10 of the
PAC Control User’s Guide
and individual commands in the
PAC Control
Command Reference
.
If you are not using PAC Control but writing your own software applications to access the Scratch Pad areas,
see the
OptoMMP Protocol Guide
. This guide is written for I/O units, but much of the same information on
programming applies to SNAP PAC controllers. The Scratch Pad areas of the memory map are described in the
programming guide’s appendix.
Communicating with Enterprise Systems and Third-Party Software
In addition to its capabilities in I/O, control, and peer-to-peer communication, the SNAP PAC R-series I/O
system can also interface directly with enterprise systems and third-party software that need to use its data.
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)
