Contec BX-M2510 Series Reference Manual page 29

 Input equivalent circuit
 When selecting inputs (an example of connecting the
product to a switch)
When the switch is "ON", the relevant bit indicates "0".
When the switch is "OFF", the relevant bit indicates "1".
 When selecting outputs (an example of connecting to the
LED)
The corresponding LED lights up when you output "1" into the appropriate bit.
The corresponding LED turns off when you output "0" into the appropriate bit.
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Product Nomenclature and Function
BX-M2510 Series Reference Manual
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