National Instruments 6008 用户手册

Exceeding the maximum input voltage ratings or maximum output ratings, which 

are listed in the 

 section, can damage the DAQ device and the computer. 

National Instruments is not liable for any damage resulting from such signal connections.

The default configuration of the NI USB-6008/6009 DIO ports is open 
collector, allowing 5 V operation, with an onboard 4.7 k

Ω 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 14. 

The NI USB-6009 ports can also be configured as active drive using the 
DAQmx API, allowing 3.3 V operation with a source/sink current limit of 
±8.5 mA. Refer to the NI-DAQmx Help for more information about how to 
set the DIO configuration.

Figure 14.  Example of Connecting External User-Provided Resistor

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.

3.

Adjust the variable resistor until the ammeter current reads as the 
intended current. The intended current must be less than 8.5 mA.

4.

Remove the ammeter and variable resistor from your circuit.

5.

Measure the resistance of the variable resistor. The measured 
resistance is the ideal value of the pull-up resistor.

GND

P0.0

+5 V

Rp

Re

Rl

NI USB-6008/6009

Load

A

+5 V

Port Pad

4.7 K

Ω Onboard Resistor

External

Pull-up

Resistor