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Analog Input Subsystem
C-13
Data Coding
The DAS-1800 converts the analog input signal data and returns its value
in an integer format. For bipolar mode, the hardware returns A/D data as
2’s complement in the range of -2048 to 2047 for 12-bit and -32768 to
32767 for 16-bit A/Ds. For unipolar mode, the hardware returns data as
straight binary. The range is 0 to 4095 for 12-Bit ADCs and 0 to 65535 for
16-Bit ADCs.
The DAS-1800 returns data in integer format for all data transfer
modes—
POLLED
,
INTERRUPT
, and
DMA
. The “native” data format of
all DAS-1800 A/D boards is integer. There are no channel “tags.” The 12
least significant bits of the word contain the 12-bit A/D data (right
justified). In bipolar mode, the four most significant bits all contain the
sign. For a 12-bit A/D at a gain of 1 in the ±10V range (bipolar mode), the
voltage resolution would be:
9
25
41
57
73
89
105
121
137
10
26
42
58
74
90
106
122
138
11
27
43
59
75
91
107
123
139
12
28
44
60
76
92
108
124
140
13
29
45
61
77
93
109
125
141
14
30
46
62
78
94
110
126
142
15
31
47
63
79
95
111
127
143
Table C-3. Table of Logical Channel Numbers for
Eight External EXP-1800 Multiplexers (cont.)
Native
Chan
Mux #
0
MUX
#1
1
MUX
#2
2
MUX
#3
3
MUX
#4
4
MUX
#5
5
MUX
#6
6
MUX
#7
7
MUX
#8
etc.
MUX
Input
Chan #
20V
4096
------------
4.88mV
=
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