Data loss in double buffered input PCI-6533 (DIO-32HS)

[Adikus]

Hi
My PCI-6533 connected to external card. I'm trying double-buffered input in burst mode. External hardware clock at 5 Mhz, group size 4. REQ and ACK signals set to active high always.
I use sample programs from NI on C.
Using single buffer mode I receive correct sequence of data.

But when I try double-buffered mode, in every half-buffer, part of input sequence is lost. It happens after 17th point from beginning of halfbuffer. So first 17 samples are continued from the end of previous half buffer. Then another sequence begins.

It does not depend on size of buffer, number of half buffers.

Any help would be appreciated.
Best regards
Adikus

[CAS]

Hi Adikus

I have had the same problem recently - losing data points every time I transfer a half-buffer when acquiring in burst mode. Some application notes I found useful from the development library were:

Measurement Hardware > Digital Input/Output > Handshaking >'Handshaking I/O Issues Using the DIO-32HS/6533 Device'

Measurement Hardware > Digital Input/Output > General >'High-Speed Digital Considerations'
and
Measurement Hardware > Digital Input/Output > General > 'Digital I/O Applications'

The problem you are having is due to the fact that you are not using the REQ and ACQ lines. The ACQ line is controlled by the PCI 6533 card and signals when the card is ready for a transfer. If you have a look at this line during acquisition you should see that
it is set low briefly each time that you transfer a half buffer.

You need to monitor the ACQ line and pause your external card from trying to input when the ACK line is low. I've added a FIFO between my instrument and the PCI 6533 card. I've found that I require this to be capable of holding 16k samples but I arrived at this value through testing alone (I am acquiring 2 bytes at 1MHz). My testing also illustrated how other activity on the PC can affect the acquisition, e.g. saving a large file would cause a pause.

I've posted a couple of questions relating to this recently too which might be useful for you to check out.

Regards,
Cheryl

[Adikus]

Thanks Cheryl.
Now it's clear for me what is going in system.
I hope PCI 6534 has no problems like this.

Adikus