PID position control : guide me

Dear member

I want to built a PID position control 

i read the DC position through potentiometer with -128 to 127 [full 360 degree]

so the input to the pid is voltage range between -128 to 127

the input of dc motor is PWM and the motor rotate direction

so the PID output will be PWM 

what about direction bit ??? What will be it circuit

also how to control the speed in same system ?? is thire another PID?? 

best regards