Module considerations – Rockwell Automation 1746-FIO4V SLC 500 Fast Analog I/O/ User Manual User Manual
Page 32
Publication 1746-UM009B-EN-P - September 2007
32 Processor and Module Considerations
Module Considerations
The module’s I/O channel converters affect resolution of I/O data and
bit usage in I/O image words. We show you how to compute I/O
signal levels. Input filtering and input A/D conversion affect input
response time.
Data Resolution of the Module’s I/O Channel Converters
The module’s I/O channel converters limit bit usage to less than a full
16-bit word when converting analog to digital input data and digital to
analog output data. Bit maps show resulting digital data storage in
input and output image words.
Bit Usage for I/O Channel Converters
The input channel converter resolution is 12 bits, where the highest
four bits are always zero. The usable range of the channel word is
0…4095.
The output channel converter resolution is 14 bits, where the lowest
two bits are not used. They have no effect on the output value.
Bits not used
Bits not used
CH 0 INPUT
CH 1 INPUT
CH 0 OUTPUT
CH 1 OUTPUT
Isb
Isb
msb
I:e.0
I:e.1
O:e.0
O:e.1
e = module’s slot number
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
msb
IMPORTANT
The module left-justifies the 14-bit data (lsb at bit 2) in the
output channel word. This reduces the output resolution to:
• 2.56348 µA/LSB for current outputs
• 1.22070 mV/SLB for voltage outputs