FATEK M Series User Manual page 20

While the various expansion modules other than the CPU module have the same printed labels on the
input/output terminals as the CPU module do, these labels are only relative I/O numbers, different from
the absolute I/O numbers on CPU module. The number of a terminal only represents its order on the
expansion module. For example, the first contact is 1, the second is 2, etc. All numbers on the expansion
module begin with 1. The actual number of digital input contact or the output replay, however, is
determined by summing the numbers on all previous expansion modules and the CPU module. See the
following figure and its calculation.
As shown in the above figure,10 output points on the 2nd expansion module M16X. Because the top X
numbers of the previous two units are 15 and 16, respectively, the number of input contact X41 on second
expansion unit should be:
Expansion Module Digital I/O Number
X( 15+16+10 ) = X41
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Chapter 2 Expansion of M-Series PLC
M-Series PLC Expansion Module User Manual