snap ethernet-based i/o units protocols and programming guide

CHAPTER 1: INTRODUCTION
The I/O Side of the Brain
The SNAP Ultimate brain reads and writes to the I/O points on the rack using its I/O side memory
map.You can think of the brain’s memory map as a grid of mailboxes, with each mailbox having
its own memory address. Each mailbox address has a specific purpose. For example, one address
holds the state of a single digital point; another address holds counter data for the same point.
The complete list of memory map addresses is in Appendix A. If you are familiar with
programmable logic controllers (PLCs), you’ll see that the memory map is similar to a register.
On its I/O side, the Ultimate brain has the same features as a SNAP Ethernet brain.
The Control Side of the Brain
In the control side, the SNAP Ultimate brain can run an ioControl strategy, a flowchart-based
control program you develop in ioControl. These flowcharts provide the logic that controls
processes through the system. Commands within the flowchart read from and write to the
memory map in the I/O side of the brain in order to monitor and control the I/O points. On its
control side, the SNAP Ultimate brain has capabilities very much like a traditional Opto 22
controller.
Using the Two Sides
Many customers who use SNAP Ultimate I/O never need to think about the I/O side and its
memory map. While the Ultimate brain has the same features on its I/O side as a SNAP Ethernet
brain, most of these features are easier to use in an ioControl strategy running on the control
side. If your only communication with the brain is through an ioControl strategy, you do not need
to use this programming guide or the memory map at all. You should use ioManager to configure
the system and ioControl for developing your monitoring and control strategy. The ioManager
User’s Guide and the ioControl guides will provide the information you need.
However, if you are using another method to communicate with the brain, either instead of or in
addition to an ioControl strategy, you need the additional information provided in this
programming guide.
Remember that because the SNAP Ultimate I/O system is so versatile, you can use several
methods at once to do several things. For example, the system might be running an ioControl
strategy, providing data to a peer on the network, and communicating with a third-party HMI, all
at once.
Any time you are communicating with both the control side and the I/O side of the brain at once,
plan carefully and use caution. The control side of the brain reads from and writes to the I/O side
just as other methods do directly. Make sure that data being written directly to the I/O side does
not conflict with control logic being executed in the ioControl strategy.
10 SNAP Ethernet-Based I/O Units Protocols and Programming Guide