I am using the 9S12XDP512 from TechArts and connecting 3 Lynxmotion Tracker Sensors to PORTA[7:5], PORTA[2:0], and PORTB[7:5]. The Tracker Sensor outputs HI for WHITE light, and LO for BLACK light. I have configured the Data Direction registers for PORTA & B (i.e. DDRA = 0x14; DDRB = 0x1F; ). Also, the MCU provides the +5VDC to power the sensors.
The problem occurs when I switch the controller to 'Run' and press the 'Reset' button. Nothing happens, until I place a WHITE sheet of paper under the PORTA sensors. Only then does the program execute. Why does my program require an external event to start?
Thanks for your help.