Specifications

Analog Input Modules
78
31007715 6/2008
Input Data
Registers
Each STB AVI 1275 data register represents the input voltage of a channel in the
IEC data format. The data has 9-bit + sign resolution. The bit structure in each data
register is as follows:
There are 10 significant bits in each data word—bits 15 through 6. They allow you
to represent voltage data with integer values ranging from -32 768 to +32 704 in
increments of 64. A value 32 000 represents +10 V and a value of -32 000
represents -10 V. When bit 15 is 0, the value is positive; when bit 15 is 1, the value
is negative.
Linear voltage is interpreted using the formula:
where Cn is the numerical count and Vai is the analog input voltage.
Values greater than 32 000 and less than -32 000 do not produce out-of-range
indications.
8
0
0=+
2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
always 0
1=-
Sign bit
STB AVI 1275 Data Register Format
12 3 45
67
910111213
14
15
V
ai
C
n
3200⁄=
V
32 704
32 000
9V
10.22 V
10 V
28 800
-9 V
-10 V
-10.24 V
-32 768
-32 000
-28 800
ai
C
n
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