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

Logging Data
Area Number
of Bytes
IEEE 1394
packet header
(without CRC)
Useful data
2 Total length of packet
For example, the first bytes of a stream packet might look like this:
CHAPTER 2: OVERVIEW OF PROGRAMMING
Description
2 First byte is zero-filled; second byte contains transaction code 0x0A for an
isochronous data block (4 bits) and synchronization code for Opto 22 use (4 bits).
256 Analog values in Engineering Units (IEEE floats). Contains 4 bytes of data for
each of 64 points, starting with point 0.
256 Point feature data (counter data) (unsigned 32-bit integers).
8 On/off state of all digital points (mask)
8 On latch state (mask)
8 Off latch state (mask)
8 Active counters (mask)
Unused data 56 Reserved for future data; zero-filled
These packet bytes: 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th
Contain this hex data: header 41 77 33 33 41 3F AC 66
For these points: -- 0 1
On module at position: -- 0
In the body of the stream packet, IEEE floats are arranged in low point/low address order. See
page 43 for an example. All masks in the stream packet are in Big Endian format, however, with
higher-numbered points in the lower-addressed byte. See page 41 for more information about
how data in a mask is formatted.
Your SNAP Ultimate or SNAP Ethernet brain includes a feature that allows data from memory
map addresses to be recorded in a log file. The data from up to 64 memory map addresses can
be logged, and all logged data is recorded in one file. The log file holds up to 300 lines of data;
when it is filled, new entries replace the oldest ones.
Logging data requires two steps:
Configure the events (Scratch Pad masks) that trigger logging and the memory map
addresses to log data from.
Read the data from the data log.
SNAP Ethernet-Based I/O Units Protocols and Programming Guide 37