Problems with 6534-External Clocking

[Ryan Fenton]

Hi,

I'm using an external clock(from a data generator) with pattern output on the 6534.I am using the onboard looping feature with a groupsize 4(32bit).

I have two main problems:

1)At frequencies above 5MHz(clock signal of 10MHz) the signals degrade greatly, square waves become irregular.This may be due to the fact that when I connect the external clock to the REQ pin the clock is distorted which may cause the signals to trigger incorrectly.Why would the clock be distorted?Drawing too much current?

2)When the clock frequency is set to anything above 17MHz the DAQ card sets the output to high and no signals are triggered.If the clock frequency is reduced the DAQ card will not trigger any signals until the block operation
is cleared and restarted.
The DAQ card should be able to work on an external clock up to 20MHz?The clock signal is a squarewave so the pulsewidth is 25ns at 20MHz which is greater the minimum of 20ns.

Thanks

Ryan

[rgharrison]

Hi Ryan,

I believe you need a cleaner clock source at the connection to the DAQ board. My suspicion is that you are experiencing reflections and transmission line effects. To help these noise issues, it is advisable to try and use the shortest length of wire possible to the 6534 board and to twist a grounded wire around your clock signal. This will help attenuate outside interference.

I've included a note describing these effects in more detail. Another option is to sample your clock on the falling edge. This is really only a consideration on data input though. Anyway, hope that helps. Have a good day.

Ron