Yamaha YIS503IIIR and Commodore 1084S-D2

I thought I'd build a cable to connect the two.

The computer has an 8-pole DIN connector labeled RGB, which I assume is identical to that of the CX5M. The pin description I found at cx5m.net is a bit sparse.

1. GND
2. Sound
3. AV
4. Y
5. YS
6. R
7. G
8. B

The monitor uses a 9-pole d-sub connector.

1. GND
2. GND
3. R
4. G
5. B
6. n/c
7. CSYNC (Composite Sync)
8. n/c
9. n/c

So I connect the R, G and B signals together, but what about "composite sync"? Is it available on the computer side?

Cheers