National Instruments DAQ 6527 Digital Filtering

Chapter 4 Device Overview

• Input ports

– Read

– Apply digital filtering (software programmable)

– Detect changes on selected lines (software programmable)

Tabl e 3- 1, Port Functionality for 6527 Devices, contains a summary of port

functions.

The digital input ports of a 6527 device are optically isolated using Infineon

IL55B optocouplers. Each IL55B provides optical isolation for one channel

of input.

Isolation on the output is provided by Infineon LH1546 solid-state relays.

One solid-state relay is used for isolation at each channel of output.

For diagrams of the complete input and output circuitry, see Chapter 3,

Signal Connections.

Digital Filtering

All of the inputs on the 6527 device contain a digital filter option. Filtering

can help eliminate glitches on input data. When used with change

notification, filtering can also reduce the number of changes for you to

examine and process.

You can configure any of the digital input channels from the optocouplers

to pass through a digital filter. You can also control the timing interval used

by the filter. The filter blocks pulses shorter than the specified timing

interval, treating them as glitches. The filter passes pulses longer than twice

the specified interval. Intermediate-length pulses—pulses longer than the

interval but less than twice the interval—may or may not pass the filter.

The filter operates on the inputs from the optocouplers. The optocouplers

turn on faster than they turn off, passing rising edges faster than falling

edges. The optocouplers can therefore add up to 100µ s to a high pulse or

subtract up to 100 µs from a low pulse (a 100µs change is typical at

IF=5 mA, RL = 100 Ω). As a result, the pulse widths guaranteed to be

passed and blocked are those shown in Table4-1.