GE PME Analog Control

I'm using a Vmax Micro 20 with an analog option module on our system. I have 2 inputs open and close. They are to control a 4-20mA motorized valve. The operator must maintain either button to open or close. When neither button is pushed, the valve maintains its position. I'm a little confused as to the best function block/logic to use.....

Thank you.........