Publication 1769-UM009B-EN-P - May 2002
6-16 Using the 1769-SDN Scanner Module with CompactLogix Controllers
Calculating I/O Usage for the I/O Modules
The formulas below are used to calculate the amount of I/O used by
each type of I/O module. The amount of I/O used by each module
will then be subtracted from the total amount of I/O supported by the
CompactLogix controller. If we calculate the amount of I/O used by
each I/O module in the CompactLogix system, except for the scanner,
then what remains is the maximum amount of I/O the scanner can
support in that particular system.
Formula for Modules with Only Input Data
The formula is:
6 words + the number of input words rounded to the next even
number
Formula for Modules with Input and Output Data
The formula is:
8 words + the number of input words rounded to the next even
number + the number of output words rounded to the next even
number
Example Calculations
These examples show how to determine the amount of data that will
be left for the scanner module.
Example 1:
The 1769-IQ16 module contains only input data, so its total I/O
count is:
6 words + 2 words = 8 total words of I/O
Since this module has only one input word, we must round up
to 2.
Example 2:
The 1769-OV16 module contains one input and one output
word, so its total I/O count is:
8 words + 2 words + 2 words = 12 total I/O words
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