Table 8-1. filters, Figure 8-4. filter example – National Instruments DAQ M Series User Manual

Page 105

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Chapter 8

PFI

© National Instruments Corporation

8-5

NI 6236 User Manual

The filter setting for each input can be configured independently. On power
up, the filters are disabled. Figure 8-4 shows an example of a low to high
transition on an input that has its filter set to 125 ns (N = 5).

Figure 8-4. Filter Example

Enabling filters introduces jitter on the input signal. For the 125 ns and
6.425 µs filter settings, the jitter is up to 25 ns. On the 2.55 ms setting, the
jitter is up to 10.025 µs.

When a PFI input is routed directly to RTSI, or a RTSI input is routed
directly to PFI, the M Series device does not use the filtered version of the
input signal.

Refer to the KnowledgeBase document, Digital Filtering with M Series, for
more information about digital filters and counters. To access this
KnowledgeBase, go to

ni.com/info

and enter the info code

rddfms

.

Table 8-1. Filters

Filter Setting

N (Filter

Clocks Needed
to Pass Signal)

Pulse Width

Guaranteed to

Pass Filter

Pulse Width

Guaranteed to

Not Pass Filter

125 ns

5

125 ns

100 ns

6.425 µs

257

6.425 µs

6.400 µs

2.55 ms

~101,800

2.55 ms

2.54 ms

Disabled

1

2

3

1

4

1

2

3

4

5

RTSI, PFI, or

PXI_STAR Terminal

Filter Clock

(40 MHz)

Filtered Input

Filtered input goes high
when terminal is sampled
high on five consecutive
filter clocks.

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