Motorola M68HC08 manual Bldc Commutation and Zero Crossing Selection

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

Software Design

5.6.2 BLDC Commutation and Zero Crossing Selection

The required BLDC motor voltage system commutation is provided using the MC68HC08MR32 PWM block.

The zero crossing selection is provided by setting port F pins

PTF1–PTF3 connected to the multiplexer.

As shown in Data Flow, the commutation and back-EMF zero-crossing selection process is split into two actions:

1.Preset BLDC commutation and BEMF zero-crossing selection

2.Set BLDC commutation and BEMF zero-crossing selection

5.6.2.1Preset BLDC Commutation and BEMF Zero Crossing Selection

In each phase of the 6-step commutation two PWM channels (bottom and top switch) are active and the other four PWM channels are logical

0.The commutation preset is accomplished by setting the buffered

registers PVAL1H, PVAL1L through PVAL6H, PVAL6L. To preset the active PWM channel, the MSB bits of the dedicated PVALxH registers are set to 0.To preset the PWM channel to the logical 0, the MSB bits of the dedicated PVALxH registers are set to 1. This is due to the signature bit functionality as described in 68HC908MR32, 68HC9908MR16 Advance Information (Motorola document order number MC68HC908MR32/D) .This commutation preset is provided by the function Commut (). In Commut(), the function field Set_PWM(P_Step_Cmt] () calls one of Shft_PWM0..5() functions according to P_Step_Cmt value, so the PVALxH registers are set as required. This will not effect the PWM signals until LDOK bit is set. Also, the back-EMF zero crossing selection preset is provided in this function, by setting V_MUX variable according to P_Step_Cmt value.

5.6.2.2Set BLDC Commutation and BEMF Zero Crossing Selection

The commutation set is provided in timer 2 interrupt function TIMACh3_Int() in the code_isr.c file. The PWMEN is toggled and LDOK bit set, in order to immediately restart the PWM generator and reload the PWM with the buffered PVAL1H, PVAL1L through PVAL6H,

Designer Reference Manual		DRM028 — Rev 0
104	Software Design	MOTOROLA
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