David,
Yes, with PhD, PhD2, or any other program that supports the ST4 interface directly from the guider (your STi has the ST4 itself - it is the modular phono jack right next to the USB cable).? Or if you like you can use an program that supports? ASCOM using a USB-to-ST4 dongle. There are several of the later available like that of ShoeStringAstronomy or ZWO. Some prefer that option because it means there is one less cable going to the OTA (but there is still one going to the mount). But it means you have to load and run ASCOM - which you may or may not already be doing. The ST4 is simpler that way.
Regards,
Mark C.
PS: To be clear - the ST4 interface, while it uses a 6P6C modular phono jack, is NOT a serial link. It is a series of 6 discrete electrical signals (one for each of N, S. E and W, one ground, and optional a power line). Just like the hand pad. If your model oft the drive has a connector marked "HD/CCD" that is the same as the hand pads connection.
PPS: You can buy 6P6C (sometimes called RJ12 or RJ11 - 6P6C refers to six position/six connections) splitters so you can have the hand pad and the guider connected at the same time.
