ECE 471                          LAB 8                            FALL 2008

PURPOSE: Learn about driving a stepper motor, interrupts on the PIC, writing 
code in C.

EXERCISE:  This program will control a stepper motor using interrupts. The
speed of the motor will be controlled by two inputs ("buttons"). Each time
one button is pressed, then the motor will increase it's speed by 10 RPM.
When the other button is pressed, the speed will decrease by 10 RPM. If the
speed becomes zero, then the motor will stop (disable the interrupt). If 
the motor speed becomes negative, then the motor will reverse direction.
Your code will be written in C.

Motor stepping must use interrupts on TIMER1. Your program will have three
main parts: initialze the interrupt, main code which checks the buttons 
and updates the RPM, and the interrupt service routine which steps the motor 
in the proper direction.

Notes:

Remember to debounce when checking the buttons (disregard time spent in the
interrupt routine when computing the delay).

When the main program determines the new RPM, it must compute the new delay 
between motor steps and store it in memory. This can either be done in a 
lookup table, or do the division using the routine given in Microchip 
Application Note #544.

Your ISR will simply step the motor in the proper direction.

The motor turns at 15 degrees per step.  Include delay calculations in your 
notebook. 

MOTOR STEPPING TABLE:
  Bit 3	  Bit 2	  Bit 1	  Bit 0
    1       1       1       0
    1       1       0       1    Read down for patterns to cause CW rotation
    1       0       1       1    Read up for patterns to cause CCW rotation
    0       1       1       1

You can initialize the motor pattern with 0xEE and then do an 8-bit rotate to
get the next pattern.

Initialize the motor output port with the pattern before making it an output.
If you make it an output first and then initialize the pattern, you can 
momentairly have all pins being one, drawing too much current.

In wiring the motor, the 4 control lines must use a wire to jumper each of the 
four outputs to the PIC. Power and ground can attach to the HC11 board (if you 
are using that for power).  On the stepper motor board GND is next to the four 
stepper motor inputs, and VCC is on the end (the end nearest the center of the 
board).  Please check with the instructor if you are not sure.

  Unused  Bit 3	  Bit 2	  Bit 1	  Bit 0	  GND	  VCC	  Board Center --->>
 

For a 90 grade do just this. For more points use features not yet covered.
Turn in the usual and anything else that is appropriate, including lab sheet, 
flowchart, schematics, timing calculations, and code.