Seth Schwiethale James Crosetto James Ellison

 square pulse of ms, repeats every 20 ms  It is the same for both steering and acceleration  width of the pulse determines the direction/speed w/ 1.5 ms as the nominal center  the amplitude of the pulse is from the reference level of the Vcc (5v)

 1 “alarm” output  max activation is 100 times/sec (increments of 10 ms)

 Camera’s output can’t produce a 20ms PWM signal that is high between 1-2ms  Car cannot be driven by Camera directly  need something that modifies the output signal of the camera so it can be used by the car

 Using a microprocessor (MC9S12DP256)  has a clock signal rate of 24MHz  has registers for a Pulse Width Modulator and an Enhanced Capture Timer  Signal from the camera can be varied between ms for speed and ms for steering

car’s input camera’s output microprocessor

 used to create correct output signal  uses CPU clock signal to generate signal lengths  current signal is 24MHz and we need a 50Hz (20ms) signal (Factor of !)

 Initializing the Pulse Width Modulator

 The pulse width modulator uses registers to decrease the frequency of the clock signal before it is used as an output signal  Two output signals can be generated from the clock signal Allows for finer control of signal

 The periods of both SA and SB need to be 20ms

 The duty cycle (the part of the PWM signal that is high) needs to be 1-2ms in length  Initialized to 1.5 ms Notice the difference!

 Used to trigger interrupts  Set up to trigger an interrupt every time a signal goes high or low on an input port (TCTL4 and TIE)

 Timer Register (TCNT) is incremented every clock cycle (24MHz clock = 24 million times per second)  Clock slowed to KHz  TCNT is 16-bit register ( )  Overflows about every 1/3 second (65535/187500)  Never overflows more than once per input signal from camera