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Motorola M68HC08 User Manual

Page 98

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Software Design

Designer Reference Manual

DRM028 — Rev 0

98

Software Design

MOTOROLA

Service of Commutation

As already explained, the motor phase commutation is performed in
the OC interrupt service routine. The phase commutated flag
(PC_F=1) indicates this action to the scheduler, which allows the
performed commutation to be serviced. Detailed explanation of this
state is in

Processes Commutation and Zero Crossing Preset and

Set

.

Service of Received Back-EMF Zero Crossing

The back-EMF zero crossing is detected by PWM middle function
block. Then the appropriate flag (captured received the zero crossing
event - ICR_F) is set by PWM centre interrupt service routine. This
indicates to the scheduler that the zero crossing event must be
served.

The following actions are taken:

1. Commutation parameters are recalculated more precisely based

on the received feedback

2. Commutation time is preset to the output compare register of timer

2

For a better understanding of how the commutation process works,
see

3.3.1 Sensorless Commutation Control

, (see

3.3.1.5 Starting

— Commutation Time Calculation

).

BEMF Zero Crossing Sensing Interrupt Service Routine

This ISR is used to evaluate the back-EMF zero crossing. Back-EMF
is evaluated here in order to synchronize zero crossing capture with
the middle of central-aligned PWM. This technique rejects the noise
caused by PWM from the back-EMF signal. When this ISR is initiated,
then three samples of the zero crossing input (BEMF_IN) are taken
and the state is evaluated. Based on the expected edge (V_TASC2,
ELS2A_ELS2B) and the evaluated state of the BEMF_IN pin, the
zero crossing event is verified. If it is accepted, then the captured time
is stored in variable (T_ZCros) and the PWM ISR is finished. The
appropriate flag (captured received the zero crossing event — ICR_F)
is set.

Current Measurement Interrupt Service Routine

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Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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