What Is the Difference Between the Terms Sinking and Sourcing?Hardware: FieldPoint, Digital I/O (DIO), Compact FieldPoint, Multifunction DAQ (MIO)
I am setting up the digital inputs and outputs in my system, and I want to make sure that I have enough current to drive the correct digital level. How do I know whether to use a sourcing or a sinking digitial I/O?
Sinking and sourcing refer to the type of digital inputs and outputs used. A sinking digital I/O (input/output) provides a ground. A sourcing digital I/O provides a voltage source.
Consider a simple circuit that consists of one digital input connected to a digital output. The circuit needs a voltage source, a ground, and a load. A sourcing digital I/O provides the voltage needed for the circuit. A sinking digital I/O provides the ground needed in the circuit. The digital input provides the load required for the circuit to work.
Figure 1 shows a sinking digital output that is connected to a sourcing digital input. In this circuit, the sourcing digital input provides the voltage and the load. The sinking digital output controls the line by using a transistor to leave the line high (at +V) or to ground the line to 0 V.
Figure 2 shows a sourcing digital output that is connected to a sinking digital input. In this circuit, the sourcing digital output provides the voltage and the sinking digital input provides the load and the ground. The digital output controls the line by using a transistor to leave the line at 0 V or to raise the line to +V.
Because you need both a voltage source and a ground in order to create a complete circuit, you need to have a sourcing input or output connected to a sinking output or input. If you wish to connect a sourcing input to a sourcing output or a sinking input to a sinking output, you will need to add an additional resistor. For further information on connecting two I/O of the same type, please refer to KnowledgeBase 2K0D6H5F attached in the Related Links section below.
KnowledgeBase 2K0D6H5F: Connecting Two Sinking I/O or Two Sourcing I/O Together
KnowledgeBase 3E6AIAFL: M Series Maximum Sink/Source Current Specifications for PFI, DIO and Counters
KnowledgeBase 1EPBH9LK: Can I Connect a Coil Relay Directly to my FP-DO-400 or FP-DO-401?
Developer Zone White Paper: Digital I/O Sinking and Sourcing
Report Date: 01/25/2002
Last Updated: 11/08/2013
Document ID: 2HOE7K5F