Whilst researching something else, I came across this useful piece of information in the SynScan v 3.35 manual (pp 36-7):
This sounds like a useful function, which could replace the PC-based DSLR Shutter or a stand-alone interval timer.
It just needs a simple cable between the camera and the RJ12 socket on the bottom of the hand-control.

Ross I think it only works on 3 mounts with a 'snap port' that have a stereo type jack socket.

AZEQ6, EQ8, Allview Az mount.

Well John according to their manuals, pins 1 & 4 on the RJ12 socket (which they call an RJ11) are used for this function:
but the control functions only seem to be implemented (from the Utility menu) in the V3 firmware.

The only other note I found is that it's "Applicable to Equatorial mounts" and "Applicable only to certain types of mounts and motor controllers".
Anyway, I've made up a lead to try out with Bill's SynScan handset when I get a chance...

yep your right. just went through the menu on my controller and the camera control is there but its a AZ goto, shows that I never read the manual fully and like you say it only works on certain mounts. Looks like on the later mounts they've tapped off them 2 wires and fitted the snap port [stereo jack] and most likely added another £50 for it.
I've not got a camera with a external port to try.

Specifications (photo/video):

•Panoramic photo modes: Easy Pano Mode, Preset Pano Mode & Time Lapse Mode
•Electronic shutter release cable: Canon D cable supplied (other cables readily available)
•Video Coursing mode: Up to 10 hours video capture between two points

I've just confirmed that this facility is present in the Synscan hand-control for Joe's HEQ5 Pro mount (this is four or five years old and is running firmware version 3.32) and I've just had it firing the shutter in my Pentax K110D.
You can set the exposure duration and number of frames in the sequence, but the pauses between exposures is fixed at 2-sec.