Use of pullup resistor in cnReach IO module

cnReach IO module provided 4 primary Digital IO channels. they are located at pin #6, #8, #10 & #12.

These 4 channels are equipped with pullup resistor. The pullup resistor, when enabled, will maintain a high voltage reading to the input pin - so when you use modbus poll to query the channel discrete input reading, you will recieve a "1" (when disabled, you recieve a "0"). You can connect a dry contact sensor (for example, a door switch) to these pin (with the other leg to the ground). When the sensor closed the circuit, the input pin will now read a "0" - because the high voltage input is directed to the ground. The following picture shows an example of how to use this feature. when the sensor switch is "openned", modbus poll discrete input will return a "1", otherwise, it returns "0".


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