Motorola M68HC08 User Manual
Page 95
Software Design
State Diagram
DRM028 — Rev 0
Designer Reference Manual
MOTOROLA
Software Design
95
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
µs
(128
µs 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
3.3.1.4 Starting (Back-EMF Acquisition)
shows 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
Starting — Commutation Time Calculation
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