FX1N Series Programmable Controllers Introduction 1.
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• If a DC powered main unit is used with a power supply of less than 24VDC -15% (20.4V DC
or less), then it 
cannot
 be fully expanded by using special function blocks or powered
extension units. 
It can accommodate a maximum of an additional 32 I/O points.
• If an FX
1N
 expansion board is being used, it does not alter the rules of expansion outlined
above, as it utilizes special M coils for its operation and therefore does not contribute to the
maximum 128 I/O point count. Only one special function board can be used at any time.
See section 3.9.1 for more details.