National Instruments NI USB-621x Connecting Digital I/O Signals

Chapter 8 Digital I/O

Connecting Digital I/O Signals

The DI and DO signals, P0.<0..7> and P1.<0..7> are referenced to D GND. Digital input applications include receiving TTL signals and sensing external device states, such as the state of the switch shown in the figure. Digital output applications include sending TTL signals and driving external devices, such as the LED shown in Figure 8-2.

	+5 V
	Isolation
	Barrier
	(USB-6215
LED	and USB-6218
	devices only)
	P1.<0..3>
	Digital
	Isolators

TTL Signal

+5 V

Switch

1

P0.<0..3>

D GND

I/O Connector

M Series Device

1When using a USB-6215/6218, you must connect D GND

and/or AI GND to the local ground on your system.

Figure 8-2.Digital I/O Connections

Caution Exceeding the maximum input voltage ratings, which are listed in the specifications document for each M Series device, can damage the DAQ device and the computer. NI is not liable for any damage resulting from such signal connections.

© National Instruments Corporation 8-3 NI USB-621x User Manual