MC68HC705MC4 Datasheet, PDF (73/99 Pages) Motorola, Inc – Microcontrollers

MC68HC705MC4 Specification Rev. 1.5
port (MEA=0, DDRA5=1). PA7 is configured as an output port (DDRA7=1). The software
moderates the PWM output pulse width based on speed feedback data obtained from a
tachometer or other such device. The tachometer would typically drive an input capture,
providing data to the MCU from which velocity and acceleration information can be
derived. The system could be modified to provide positional data for servo applications.
The truth table shown in Table 9-2: DC Brush Motor Truth Table defines the H-bridge
drive requirements for the motor from which the software would select based upon other
system inputs.
The MC68HC705MC4 can be configured to drive two motors using both PWM channels.
9.8.2 DC BRUSHLESS MOTOR INTERFACE
A typical interface for a single DC brushless motor is shown below although many other
configurations are possible. The rotor sensor usually consists of a Hall effect sensor,
optical encoder, or back-EMF detector. The coil current feedback is shown to be linear in
B+
PA6
PA4
PA2
PWMA
PA5
PA3
PA1
AD0
A
Current/Torque
Feedback
A
R_sense
0V
B
C
PB7
PB6
PB5
Rotor position
Sensor
3-phase
Brushless
DC Motor
this example, using the on-chip A/D to provide torque data to the MCU. Other systems
may only require a current limit, which could be achieved with an interrupt pin (which will
offer some hysteresis) and an external amplifier. With some reorganization of the I/O, it is
also possible to configure the device to drive two brushless motor simultaneously
MOTOROLA
Page 64
Section 9: Pulse Width Modulator