The point of the pic is an alternitive clock, the data sheet stats "that if more than L297 is connected then the clocks should be connected to syncronise the circuit", just to the right of the pic is a change over jumper one side grounds pin OSC on the L297 the other wires in the RC oscilliator components 22k and 3n3F. the pin of the pic which is wired to the (top) of v ref pot is a pullup and will have no effect in modulating Vref or anything else
Roger