8

Digital I/O

NI 621x devices have eight static digital input lines, P0.<0..7>. These lines also can be used as PFI inputs.

NI 621x devices have eight static digital output lines, P1.<0..8>.These lines also can be used as PFI output. By default the digital output lines are disabled (high impedance with a 47 kΩ pull down resistor) on power up. Software can enable or disable the entire port (software cannot enable individual lines). Once the port is enabled, you can individually configure each line to the following:

•Set a line to a static 0

•Set a line to a static 1

•Export a timing output signal to a line as a PFI pin

The voltage input and output levels and the current drive level of the DI and DO lines are listed in the NI 621x Specifications. Refer to Chapter 10, PFI, for more information on PFI inputs and outputs.

Figure 8-1shows the circuitry of one DI line and one DO line. The following sections provide information about the various parts of the DIO circuit.

Static DI

I/O Protection

P0.x

 

47kΩ Pull-Down

 

Static DO

I/O Protection

P1.x

 

47 kΩ Pull-Down

 

Figure 8-1.M Series Digital I/O Circuitry

The DI terminals are named P0.<0..7> on the NI 621x device I/O connector. The DO terminals are named P1.<0..7> on the NI 621x device I/O connector.

© National Instruments Corporation

8-1

NI USB-621x User Manual