D
3-
-0
4A
D
4-
C
ha
nn
el
A
na
lo
g
In
pu
t
2--10
D3--04AD 4-Channel Analog Input
R001
MSB
LSB
0
1
0
0
1
7
-- analog data bits
The first register contains 8 bits which
represent the analog data in binary
format.
Bit
Value
Bit
Value
0
1
4
16
1
2
5
32
2
4
6
64
3
8
7
128
Since the module has 8-bit resolution, the analog signal is converted into 256
“pieces” ranging from 0 -- 255 (2
8
). For example, with a 1 to 5V scale, a 1V signal
would be 0, and a 5V signal would be 255. This is equivalent to a a binary value of
0000 0000 to 1111 1111, or 00 to FF hexadecimal. The following diagram shows how
this relates to each signal range.
+5V
1V
0
255
1V -- 5V
20mA
4mA
0
255
4 -- 20mA
Each “piece” can also be expressed in
terms of the signal level by using the
equation shown. The following table
shows the smallest signal levels that
could possibly result in a change in the
data value for each signal range.
H = high limit of the signal range
L = low limit of the signal range
Resolution = (H--L)/255
Range
Highest Signal
Lowest Signal
Smallest Change
1 to 5V
5V
1V
15.6 mV
4 to 20mA
20mA
4mA
62.7
m
A
Now that you understand how the module and CPU work together to gather and
store the information, you’re ready to write the control program.
Analog Data Bits
