6120 counter max frequency

[windwalker]

I am trying to set the max frequency for PCI-6120 counter. By the card specification, the counter's max source frequency is 20MHz. However, on MAX software test panel, if the counter frequency is set greater than 5MHz, program pops up an error stating the max valid value is 5e6 MHz.. Attached is the error message. Did I do anything wrong? Or special card setting is needed. Please help. Thanks very much.

[Paul-D]

Hi, this is Paul with Applications Engineering at NI.

The short non-technical answer to your answer is that the maximum frequency you can generate off this card's 20Mhz timebase is 5Mhz, so this behavior is expected.

The longer answer is that a pulse trains uses 2 different registers to construct the width and the delay of your pulse.  When you configure for pulse genration, the counter continuosuly outputs pulses with these specs.  Given that the minimum pulse spec value is 2, the maximum frequency the counter can generate is the maximum internal timebase (20Mhz in this card's case) divided by 2.

A little further explanation of this can be viewed at (http://digital.ni.com/public.nsf/allkb/E9C9C56112ECEEA38625749D005A1471?OpenDocument)

Regards

[John_P1]

Hi windwalker,

The max source frequency is 20 MHz. The source is an input to the counter which is divided down to produce the output signal:

   

The default behavior is that the counter will count to N, and then toggle its output.  N must be at least 2, so the maximum frequency you can generate with the default (toggle) mode is 5 MHz (2 ticks high, 2 ticks low of the 20 MHz maximum source).

The other mode is "pulse" mode, where the counter will count to N and then a pulse its output.  You can end up getting a pulse every 2 ticks of the source, which could give you a 10 MHz clock.  You can't set this mode in the test panels, but here's an example in LabVIEW showing how to get a 10 MHz output (the "External Clock" can be the 20 MHz timebase).

However, if you're just trying to generate a 10 MHz continuous output, then I suggest using the Frequency Output which is a 4-bit counter that can output a small set of frequencies including 10 MHz -- {10 MHz,100 kHz} / {1:16}.  It is programmed similar to the other counters.

Best Regards,