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

CHAPTER 4: USING THE IEEE 1394-BASED PROTOCOL
Response packet or a Write Response packet. The structure and parameters of the request and
response packets are shown beginning on page 93.
Writing Data
To change the configuration or status of an I/O point, to enable a counter, or to write other data,
the host sends a Write Request packet containing the destination address and the new data to
be written. The SNAP Ethernet-based brain responds by returning a Write Response packet
indicating success or failure.
Reading Data
The host can also access the status of I/O modules, counter values, and other data by reading
the appropriate memory locations from the SNAP Ethernet-based brain memory map. The host
computer simply sends a Read Request packet asking for data from those memory locations, and
the brain returns the data in a Read Response packet.
The following diagram shows a specific example of a host computer reading data from a SNAP
Ethernet-based brain:
Streaming Data
Most communication involves the two-step process of request and response. But the SNAP
Ethernet-based brain can also stream data, as explained on page 35. Streaming uses UDP and
does not require a response.
For more information on using streaming, see page 88.
SNAP Ethernet-Based I/O Units Protocols and Programming Guide 81