shared timebase with USB-6211 devices

[bef]

Hi,

I'm trying to synchronize 2 NI USB-6211 devices (dev1: Master, Dev2: slave).
The tricky part is that I need different sampling rates.

Now I tried to route the 20MHz timebase to PFI4 on Dev1. Ok, I get something like a LVDS signal on the PFI4 pin. (2.3V mean, 1Vpp)
Then I wired (hardware) PFI4 of Dev1 to PFI0 on Dev2.

In LabVIEW I tried to use PFI0 (Dev2) as external timebase for AI-aquisition (Timing-Property:SampleClock:timebase:clk). Without success.

What am I doing wrong? I cound't find any hint in the docs about the signal type on an external clock. Are external clocks supposed to be TTL (0-5V)? If so, why is the "exported timebase"-signal on Dev1 LVDS? Do I have to convert this LVDS-type signal to TTL before feeding it back into Dev2 as external clock signal?

[PaulFS]

Hi bef,

as written in the USB-6211 manual (http://www.ni.com/pdf/manuals/371932e.pdf) the DO delivers between 2,7 and 3,8Volts depending on the current level.
So, you won't get 5Vs in that way (btw TTL does not mean exactely 5Vs).

Why don't you use PULL-UP Resistors to get a fine 5V HIGH State? That should work.

Kind Regards
Paul