NI USB-6008/6009 User Guide and Specifications 18 ni.com
Source/Sink Information
The default configuration of the NI USB-6008/6009 digital I/O ports is open collector, allowing 5 V
operation, with an onboard 4.7 kΩ pull-up resistor. An external user-provided pull-up resistor can be
added to increase the source current drive up to a 8.5 mA limit per line as shown in Figure 15.
1
Figure 15. Example of Connecting an External User-Provided Resistor
The NI USB-6009 ports can also be configured as active drive using the NI-DAQmx API, allowing 3.3 V
operation with a source/sink current limit of ±8.5 mA. For more information about how to set the DIO
configuration, refer to the KnowledgeBase document, Configuring NI Devices to be Open-Drain (Open
Collector) or Push-Pull (Active Drive). To access this document, go to
ni.com/info and enter the
Info Code ex52sp.
Complete the following steps to determine the value of the user-provided pull-up resistor:
1. Place an ammeter in series with the load.
2. Place a variable resistor between the digital output line and the +5 V supply.
3. Set P0.0 to high.
4. Adjust the variable resistor until the ammeter current reads as the intended current. The intended
current must be less than 8.5 mA.
5. Remove the ammeter and variable resistor from your circuit.
6. Measure the resistance of the variable resistor. The measured resistance is the ideal value of the
pull-up resistor.
7. Select a static resistor value for your pull-up resistor that is greater than or equal to the ideal
resistance.
8. Reconnect the load circuit and the pull-up resistor.
1
This document uses NI-DAQmx naming conventions. Open-drain is called open collector and push-pull is called active drive.
GND
P0.0
+5 V
Rp
Re
Rl
NI USB-6008/6009
Load
A
+5 V
Port Pad
4.7 kΩ Onboard Resistor
External
Pull-Up
Resistor
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