Motorola M68HC08 - Manual (Page 83)

Software Design
Main Software Flowchart
DRM028 — Rev 0 Designer Reference Manual
MOTOROLA Software Design 83
3.2.5 Back-EMF Sensing Circuit .The zero crossing selection is
provided by the multiplexer setting.
As shown in Figure 5-2 , the commutation and back-EMF zero crossing
selection process is split into two actions:
• Preset commutation and zero crossing selection
• The preset means setting the buffered registers and RAM
variables for commutation
• Set commutation and zero crossing selection
• The setting means loading the registers with buffered variables
The implementation is described in Implementation Notes - 5.6.2
BLDC Commutation and Zero Crossing Selection .
5.4 Main Software Flowchart
The main software flowchart incorporates the main routine entered from
the reset and interrupt states. The main routine includes initializing the
MCU and the main loop. The flowcharts are shown in
Figure 5-4 ,
Figure 5-5 , and Figure 5-6 .
MCU Initialization is entered only after system reset. It provides
initialization of system registers, ports, and CPU clock. The MCU
Initialization is provided in MCUInit() function.
After MCU Initialization the Application Initialization is executed as
AppInit() function, which performs the following actions. First the zero
current offset of the dc-bus current measurement path is calibrated. This
offset on the ADC input should be 1.65 V at zero current. This is
implemented in the hardware design, in order to be able to measure
negative and positive current values. The status registers are initialized
and PWM generator is started. Also, timer 1 is started at the right
moment to be synchronized with the PWM generator. This way the
current measurement is executed at the defined moment of the PWM
signal.
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