Motorola M68HC08 manual Service of Commutation, Set, Commutation Time Calculation

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

Software Design

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

Designer Reference Manual		DRM028 — Rev 0
98	Software Design	MOTOROLA
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