Relays, Memory Areas and Constants
1-22
External input relay (X) and External output relay (Y)
Only relays with numbers actually allocated to input contacts can be used as external
input relay (X).
Only relays with numbers actually allocated to output contacts can output as external
output relay (Y). The external output relays (Y) which are not allocated can be used as
internal relays.
Allocation of numbers is determined by the combination of units and boards used. For
details about the I/O allocation, refer to “Hardware Manual” of each PLC.
Example: FP2
0 1 2 3 4 (Slot No.)
Y10 to Y1F
X0 to XF
Power supply
unit
CPU
16−point type
input unit
16−point type
output unit
The 16 points external input relays X0 through XF are allotted
for the 16-point type input unit for slot 0, and the 16 points
external output relays Y10 through Y1F are allotted for the
16-point type output unit for slot 1.
The 16 points X10 through X1F cannot be used in this such
combination.
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