6601 sample and hold

[BonaBona]

Hi,

I have a probe set in quadrature count mode. I have it connected to an SCB-68, which is in turn connected to a PCI-6601 card. I am using a C program to read the counter values from this probe.

I also have a swinging arm (parallel to the floor) mounted on a rotary encoder which is connected to an MID-7652 box, which is in turn connected to a PCI-7342 card, used to control the servo motors to move the swing-arm. The 6601 and 7342 card are connected by an RTSI cable. The idea is to read the probe counter value while the arm is swinging about its pivot in order to measure surface profiles. It is important to know the exact arm position when the probe is read, and so latency is an issue. I am able to create an use breakpoints for the swing-arm.

Since latency is an issue I am looking to trigger a reading of the probe counter every time the arm reaches a breakpoint. I can do this using a C program but there is a delay between the breakpoint being reached when the arm reaches a breakpoint and the probe being read while the software executes lines of code.

How can I use the breakpoint output from the 7342 as a trigger to latch the value of the counter of the probe 6601 onto one of the NI-TIO registers?

Thanks

[BonaBona]

I forgot to mention, I would like to latch the probe counter reading onto the 6601 via the RTSI cable from the 7342 breakpoint output.

[hicksc]

Hi Bona

Have you been able to make any progress with this?

Kind Regards

[BonaBona]

Hi Chris,

I have tried to program a breakpoint output from the PCI-7342 board into the RTSI using the following function:

flex_select_signal(boardID, NIMC_RTSI4, NIMC_BREAKPOINT2);

Breakpoint 2 is the correct breakpoint output because my swing-arm is on axis 2 and I have been able to detect the output from pin 2 on the BP socket on the MID-7652 box.

However I am unable to detect anything in the corresponding RTSI pin (I have checked the pin connections diagram for a PCI board) using a multimeter or an oscilloscope. Please help!

Once I am able to detect something I am planning to program the input of the PCI-6601 using:

Select_Signal(1, ND_TRIGGER, ND_RTSI4, ND_LOW_TO_HIGH);

Is this the correct function to use?

As for latching the counter value into the save register, I haven't thought properly about that part yet. My thinking is that I will need to operate ina buffered mode. Is that correct?