Advanced Parallel I/O - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 347

bset PTJ,$01 ; “

bset PTJ,$01 ; “

bset PTJ,$01 ; “

bset PTJ,$01 ; “

bset PTJ,$01 ; “

bra loop ; to complete the D/A conversion

; org $FFFE ; uncomment this line for CodeWarrior

; dc.w start ; uncomment this line for CodeWarrior

end
The C language version of the program is as follows:
#include “c:\cwHCS12\include\hcs12.h”
void main(void)
{

DDRB

5 0xFF;

// configure PORTB for output

DDRJ | 5 0x03; // configure pins PJ1 , PJ0 for output

PTJ & 5 0xFD; // pull the signal A/B to low to select channel A

while (1) {

PORTB 15 1;

PTJ & 5 0xFE; // generate a rising edge

PTJ | 5 0x01; // “

PTJ | 5 0x01; // use dummy statements to provide 2 µs

PTJ | 5 0x01; // time for D/A conversion to complete

PTJ | 5 0x01;

PTJ | 5 0x01;

PTJ | 5 0x01;

PTJ | 5 0x01;

PTJ | 5 0x01;

PTJ | 5 0x01;

PTJ | 5 0x01;

}

}

▲
The AD7302 can be used to generate many interesting waveforms. Several exercise problems
are given on the applications of this DAC at the end of the chapter.

7.11 Stepper Motor Control

Stepper motors are digital motors. They are convenient for applications where a high degree
of positional control is required. Printers, tape drives, disk drives, and robot joints, for example,
are typical applications of stepper motors.

7.11.1 Principles of Rotation for the Stepper Motor
In its simplest form, a stepper motor has a permanent magnet rotor and a stator consisting
of two coils. The rotor aligns with the stator coil that is energized. By changing which coil is
energized, as illustrated in the following figures, the rotor is turned.
In Figure 7.37a-d, the permanent magnet rotor lines up with the coil pair that is energized.
The direction of the current determines the polarity of the magnetic field, and thus the angular