Using 6533, how can I wait on REQ after latching ACK?

[DMcAndrew]

This seems like it should be fairly straightforward but I can't seem to get it. Does anyone know how I can wait for a pulse on the REQ line (using a PCI-6533 DIO board)? The catch is that the DIO board needs to pulse the ACK line before looking for a transition on the REQ line and I cannot reconfigure the port in time to read the REQ latch.

I am trying to: 1)set port data; 2) pulse ACK low (~100us); 3) wait for REQ pulse low (~100us); 4)read port data.

Thank you for any help you can provide.

[Jesse_O]

Hello DMcAndrew,

Typically for common handshaking type applications (burst, 8255), the acq and req lines are controlled automatically.  However it seems like you would like to control these lines yourself.

It is possible for you to control acq with a software timed output.  I have attached an example that does this with DAQmx.  Since the control of the acq/pfi line is software timed, it would be difficult to ensure that the acquisition task does not start before the generation task (pfi2) goes low without missing a trigger.  Perhaps you could wire the output from pfi2 and your req signal back to a digital lines where a pattern match for a start trigger would wait for acq and req signals to go low.

If you are just starting a new application and you are using the PXI or PCI 6533 I would recommend that you upgrade to DAQmx.  There is also a new help file for DAQmx here.

I hope this helps.

Jesse O.
Applications Engineering
National Instruments