OPTO 22 SNAP-PAC-R1 User Manual page 29

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.
SNAP PAC R-series
I/O Unit
Control Side
Run PAC Control flowcharts
Shared tag
database
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.
CHAPTER 3: SYSTEM INFORMATION
I/O Side
Read/write to points
using Memory Map
Fixed memory area
(I/O point data)
Scratch pad area
(strategy variable data)
SNAP PAC R-Series Controller User's Guide
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
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