Motorola M68HC08 manual Back-EMF Acquisition State, Starting Commutation Time Calculation

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

Software Design

State Diagram

the over-current detection. The CMD_F (current measurement done) flag indicates that the new value of dc-bus current is ready to be processed by the current controller.

The time-out (software timer 3) of this state is defined in the software by the constants: PER_T_ALIGN and PER_BASE_T3_ALIGN.

Current Controller

The current controller subroutine is called every PER_CS_T1_US ∝s (128 ∝s with default software setting) after a new value of the dc-bus current has been obtained (CMD_F=1). It sets all six PVALx register pairs to get the right PWM ratio for the required current.

Timer 1 Interrupt

Once the synchronization of OC function with the PWM cycle has been achieved, it must be maintained because the current measurement is initiated here.

Over-Current Detection

The dc-bus current is periodically sensed and the over-current condition is evaluated. After a defined number successive over-current events I_CNTR_OVC, the control flow enters into the fault state.

5.5.5 Back-EMF Acquisition State

The back-EMF acquisition state provides the functionality described in

3.3.1.4Starting (Back-EMF Acquisition) and 3.3.1.5 Starting — Commutation Time Calculation. Figure 5-10shows the state transitions for the state.

First Commutation

After the align state time out expires, voltage is applied to another phase pair. The first commutation is made and the PWM duty cycle is constant. This value has been defined by the current controller during the Aalign state.

The calculation of the commutation time is explained in 3.3.1.5

Starting — Commutation Time Calculation.

DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	Software Design	95
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