Detect and Recover with Digital I/O Watchdogs

NI digital I/O watchdogs provide protection against a wide variety

of fault conditions:

• Computer crash – total OS crash

• Application crash – software application ceases to respond

• Driver crash – device driver ceases to respond

• PCI bus failure – communications cease to respond

With watchdogs, the digital outputs go to a safe state when a fault

condition is detected and the watchdog timer expires for safe recovery.

Watchdogs are important whenever the device is connected to actuators

such as pumps, valves, motors, and relays. The digital I/O device monitors

the software application and, if it fails to respond within the time limit,

automatically sets the output lines to a user-defined safe state. The device

remains in the watchdog state until the watchdog timer is disarmed by

the application and new I/O values are written, an NI 6509 is reset, or

the computer is restarted.

Trigger Your Application with Change Detection

With change detection, you can automatically trigger your software

application to perform a digital read operation upon a digital change

of state. A digital change of state is defined as the rising edge (0 to 1

transition) or falling edge (1 to 0 transition) on one or more digital lines.

Using change detection, you can monitor for digital events with minimal

processor usage. No polling is necessary because the digital I/O device

generates an interrupt to automatically wake up your application.

Using NI-DAQmx software technology, an NI 6509 notifies the software

application when the event is detected, causing the application to

automatically perform a read operation. To minimize the effects of noisy

input lines, you can use programmable input filters in combination with

change detection to eliminate spurious change detection events caused

by noise or glitches. NI-DAQmx also includes multithreaded streaming

technology so digital change detection events can occur independently

of other data acquisition activities such as analog input or output events.

Eliminate Noise with Programmable Input Filters

Programmable input filters remove noise, glitches, and spikes on inputs,

as well as provide debouncing for digital switches and relays. This is

important for applications in noisy industrial environments to prevent

false readings caused by noise. You can configure the programmable

input filter for each digital line by setting the filter time in seconds. Any

digital noise, glitch, or spike that is shorter than half of the specified

filter time is blocked by the digital I/O device, preventing invalid readings

and false triggers for change detection events.

Software

NI-DAQmx Software Technology

NI 6509 devices require NI-DAQmx 7.1 or later. NI-DAQmx software,

included free with an NI 6509, is available for download from

NI digital I/O device in LabVIEW, ANSI C, Microsoft Visual C++, and the

Microsoft .NET languages C# and Visual Basic .NET.

With NI-DAQmx technology, you have access to the full functionality

and state-of-the-art hardware technology of your NI 6509 digital I/O

devices. NI-DAQmx technology speeds up your development with many

features such as automatic code generation to make configuration and

programming easy. NI 6509 devices take full advantage of key NI-DAQmx

Low-Cost Industrial Digital I/O – 5 V TTL/CMOS

2

BUY ONLINE at ni.com or CALL 800 813 3693 (U.S.)

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Data Control

MiniMITE 1

FPGA

Voltage

Supervisor

Voltage

Regulator

Oscillator

Flash

CPLD

Figure 1. NI 6509 Hardware Block Diagram