How to connect ADAT? VS700 + Motu 828es

Hi, I have a new MOTU 828es.  It has digital in.  I also still have a VS700, it has digital out.  I want to connect VS700 digital out to the MOTU digital in.  When I connect via optical cable, I don't get sound.  
 
The VS700 doesn't want to clock sync with Motu.  I set the clock to external, but it doesn't sync.  Do I need to connect also out from Motu -> VS700 in to get sync?
 
Anything else I'm doing wrong?  I have no experience with digital in/out.
dave 

Hi Jim, thanks.  I feel like I have done that all that.  I actually want the Motu to be the master (since it is the interface I'm using for record/playback) and would like the VS700 to just output the audio to the Motu.  Can I go the opposite direction as you say and still have the Motu as the record/playback?
 
I have the Motu as the master world clock, set the input as ADAT for 8 ch (4 stereo).  The VS700 has its clock source as external.  The VS700 will receive signal from a mic, but it's not going to the Motu.  The indicator for digital clock source on the VS700 unit just blinks, I think it's supposed to be solid.
 
There are also SPDIF ins/outs on both units, I haven't tried that yet.  Will that connection also sync the clock?

Always wondered why the call is word-clock.

poetnprophet

Jim Roseberry
If you want the MOTU to be the word-clock Master, you need to run a toslink cable from the MOTU to the VS700.
The reason you're not hearing anything... is because the VS700 isn't getting any external word-clock.
This is actually a good thing.  
Back in the day, when some pieces of gear lost word-clock sync (like the Yamaha O1v), it would output full code white noise... which could blow monitor tweeters.

So, I need 2 connections?  [VS700 out > Motu in].....and [Motu out > VS700 in]?  that's kind of what I was thinking, but I don't want to "blow" anything, either.

If you want the MOTU to be the word-clock "Master", yes... you need two cables.
The VS700 feeding the MOTU (to send the audio)… and the MOTU to the VS700 (to feed the VS700 word-clock from the MOTU).  Otherwise, the VS700 is running on Internal word-clock... or is receiving no external word-clock (which is the case without the second toslink cable MOTU>VS700).
 
If you left the VS700 as the word-clock Master, you would be fine with a single cable VS700>MOTU.
Word-clock is imbedded with optical S/PDIF and Lightpipe.
The MOTU would need to look to its optical input for word-clock.
 
The thing you have to avoid is having both the VS700 and MOTU each on their own (separate) word-clock.
Whenever you merge two digital audio streams (each on separate word-clock), there will be small pops/ticks in the audio.  Some audio interfaces like the UA Apollo can resample the digital input (in realtime)… but most can't.

Looking at the back panel, the VS ADAT is Digital 2.

Yup, we got it.  Works now with SPDIF out from VS to in on the motu.  I wish I could get ADAT so I could have separate channels, but doesn't seem like that will work.  For now this will work.
 
thanks again everyone for the help!
dave