DIO Setting clock source (6509)

[Norick17]

I do have the PXI-6509 device to sample several digital inputs. It seems that the acquisition time to sample the SPI signals (clk, cs, mosi, miso) is not high enough to capture all rising (falling) edges of the SPI-Clock for example. The SPI is running with 1MHz which is not very fast too.

I tried to enable/disable the digital filter without success.

Questions:

• How can I set or change the sample clock used for the PXI-6509
• What is the maximal possible data acquisition time for this card? I suppose 400ns - right
• Is it possible to attach an external clock source or use an internal PXI clock?
• Other ideas to measure 1MHz SPI data?

thanks in advance

[crossrulz]

A PXI-6509 cannot do hardware timing.  You are limited by your software.  To properly sample things at several MHz, you will want to go with something more like a PXI-6508 (10MHz), PXIe-6536 (25MHz), or PXIe-6537 (50MHz).  Do note that the PXI-6508 is close to obsolescence.  I only included it in this list in case you were still using a PXI chassis instead of a PXIe chassis.

[Norick17]

Thats pretty bad news. What is the maximal possible frequency which can be used by the Software? Again, I only want to sample 1MHz max. I am using a PXIe Chassis.

[Norick17]

What is the maximal possible frequency which can be used by the Software?

[crossrulz]

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@Norick17 wrote:
What is the maximal possible frequency which can be used by the Software?

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If you are really lucky, you might be able to get up to 1kHz.  But the rate will have a lot of jitter and not reliable at all.

[Norick17]

hmmm so I am wondering what is the purpose of such card if you only can measure up to 1kHz!? 

[GerdW]

Hi Norick,

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@Norick17 wrote:

hmmm so I am wondering what is the purpose of such card if you only can measure up to 1kHz!? 

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There are a lot of situations where you only need to read DI channels at less than 100Hz…

The general answer is: first you have to write down your requirements, then you need to select appropriate DAQ hardware. (It seems you went this way in the wrong direction.)

[crossrulz · Accepted solution]

The 6509 is one of my favorite cards.  Its purpose is static DIO.  This means it is for DIO that are not constantly changing.  It could be controlling a relay, a power switch in a unit, read a status line, etc.  But you are trying to measure a communication bus.  For that, you need a high speed DIO card.