Spent some time on this over the last few days, so I thought I would post the results here in the hope that it would be of use to others in the future. First of all the equipment;
Apple MacBook Air running 0SX 10.11.5.
Pluggable USB to serial adaptor using the Pluggable PL2303 (latest) driver.
Synscan 3 AZ GOTO telescope mount.
Starrynight Pro 7.
Install the USB to serial adaptor drivers as instructed, plug in the adaptor, and reboot the computer.
Check the driver has installed properly by going to “About this Mac”—>“System report”—> and selecting the USB option on the left. You should see an item listed as “USB serial controller D”.
Next go to “System preferences”—>”Network” and highlight the USB controller on the left. In the configuration box it should say ” default”. The other boxes should be blank.
Next go to “Advanced…”in the bottom right-hand corner and input the following into the relevant boxes:
Vendor = Null Modem
Model = 9600
Dial mode = ignore dialtone when dialling.
Un-tick “enable error correction and compression in modem”.
Select “Tone” for dialing and “on” for sound.
Click ok and exit “System preferences”.
I’m not sure how relevant all the selections are, but I have included them purely for completeness sake.
Connect the telescope mount to the adapter with the recommended cable, power it up, and carry out your usual alignment procedure. When this has been completed leave the handset as it is. DO NOT PUT THE HANDSET IN PC MODE.
Fire up SNP7, open the “Telescope Control” panel, and select “configure”. For the connection box you should have the option of choosing “usbserial”. Choose the scope and mount type you require and click ok.
Now select “connect”, and the telescope should start slewing around to match up with the software.
I am not suggesting that this will work in all cases, but I have everything is working just fine and I hope it will be of some help to others.