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

CHAPTER 4
Chapter 4
Using the IEEE 1394-based
Protocol
Memory Mapping
This chapter shows you how to use Opto 22’s IEEE 1394-based memory map protocol to write
your own applications for direct communication between a PC and a SNAP Ethernet-based I/O
unit, for example, if you are writing your own driver. (Information on the Opto 22 SNAP Ethernet
I/O Driver Toolkit, which makes programming easier for Microsoft Windows users, is in Chapter
3.)
This chapter assumes the following:
Your Ethernet network—including a PC, hubs if needed, and one or more SNAP
Ethernet-based I/O units—is already installed. (For help installing and troubleshooting
your SNAP Ethernet-based I/O units, see Opto 22 form #1460, the SNAP Ethernet-based
I/O Units User’s Guide.)
Unique, appropriate IP addresses have been assigned to the brains.
Each SNAP Ethernet-based brain can be reached by the host PC using the PING program.
This chapter also assumes that you are familiar with programming, TCP/IP or UDP/IP, and
Ethernet networking. If you are not familiar with these subjects, we strongly suggest you consult
commercially available resources to learn about them before attempting to program applications
for SNAP Ethernet-based brains.
The complete SNAP Ethernet-based brain memory map is in Appendix A, starting on page 103.
This memory map covers all possible addresses; some may not apply to the brain model you are
using. For detailed information on brain models and features, see “SNAP Ethernet-Based Brain
Comparison Chart” on page 6.
The SNAP Ethernet-based brain uses the IEEE 1394 specification to provide a standard for
reading and writing data. You do not need to read the specification in order to use the protocol,
however.
IEEE 1394 specifies a memory-mapped model for devices on a serial network. For asynchronous
transfers, it also specifies a request-response protocol for read/write operations. Basically, each
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