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

CHAPTER 2: OVERVIEW OF PROGRAMMING
Float calculation: (-1) Sign x [1 + Significand/2 23 ] x 2 (Exponent-127)
Example for Opto 22 memory map
At this address: base address base address + 1 base address + 2 base address + 3
This hex data: 41 77 33 33
In binary: 0 100 0001 0 111 0111 0011 0011 0011 0011
In these bits: 31 30 . . . 23 22 . . . 0
Equals (in decimal): 0 130 7,811,891
Representing: Sign Exponent Significand
Decimal = (-1) 0 x [1 + 7,811,891/2 23 ] x 2 (130-127)
= 1 x [1.931] x 8
= 15.45 (rounded to 2 decimal places)
Two-Channel Analog Modules
Remember that the memory map is set up for four points per module. If the SNAP analog modules
you are using have only two channels, the addresses for the upper two points in each module
will not contain data.
For example, to read all bank analog point values in scaled units, you would read 256 bytes
starting at address FFFFF0600000. Here’s how data for two-channel modules in positions 0
and 1 would appear:
Beginning Address Ending Address Module Point Data Format
FFFF F060 0000 FFFF F060 0003
0 four bytes—IEEE float
FFFF F060 0004
FFFF F060 0008
FFFF F060 0007
FFFF F060 000B
0
1
2
four bytes—IEEE float
(no data)
FFFF F060 000C FFFF F060 000F 3 (no data)
FFFF F060 0010 FFFF F060 0013
4 four bytes—IEEE float
FFFF F060 0014
FFFF F060 0018
FFFF F060 0017
FFFF F060 001B
1
5
6
four bytes—IEEE float
(no data)
FFFF F060 001C FFFF F060 001F 7 (no data)
44 SNAP Ethernet-Based I/O Units Protocols and Programming Guide