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

Scaling
CHAPTER 4: USING THE IEEE 1394-BASED PROTOCOL
Scaling applies to analog points only. To scale a point, see the memory map area “Analog and
Digital Point Configuration Information—Read/Write” on page 125. Write to the point’s
addresses for high scale and for low scale. For example, to scale point 2, you would write the
high-scale float starting at the address FFFFF0C00094 and the low-scale float starting at
FFFFF0C00098.
Minimum and Maximum Values
SNAP Ethernet-based I/O units with analog capability automatically keep track of minimum and
maximum values on analog points. You can read the values at any time, for example, to record
minimum and maximum temperatures. You can:
Read min/max values for individual points
Read a bank of points
Read and restart min/max values for individual points.
To read min/max values for individual points, see the memory map area “Analog Point
Read—Read Only” on page 123, and use the Min Value or Max Value starting address for the
point you want to read. For example, you would read the minimum value for point 2 starting at
address FFFFF0A00088.
To read min/max values for a bank of points, see the memory map area “Analog Bank
Read—Read Only” on page 120. The starting address for reading minimum values is
FFFFF0600200. For help in interpreting this data, see “IEEE Float Data” on page 43.
To read and restart min/max values for individual points, see the memory map area
“Analog Read and Clear/Restart—Read Only” on page 133. For example, if you want to record
the maximum temperature at point 0 in each 24-hour period, the values must be reset when they
are read each day. You would read and restart the maximum value for point 0 using the starting
address FFFFF0F80100.
Offset/Gain
Offset and gain apply to analog input points only. To have the brain calculate offset and gain, use
the memory map area “Analog Point Calculation and Set—Read Only” on page 131. Calculate
offset first, then calculate gain.
For example, calculate offset for point 1 by reading addresses FFFFF0E00004 through
FFFFF0E00007. Calculations are completed in the background, and the response gives the offset
in counts. Next, calculate gain for point 1 by reading addresses FFFFF0E00104 through
FFFFF0E00107. Response for gain is in percent.
Since the purpose of the read request is simply to have the offset or gain calculated so that
values you read later will be accurate, you can normally ignore the response data.
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