ST72141K2 datasheet(57/132 Pages) STMICROELECTRONICS

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ST72141K

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MOTOR CONTROLLER (Cont’d)

Table 19. MTIM Timer-related Registers

Note on using the auto-updated MTIM timer:

The auto-updated MTIM timer works accurately

within its operating range but some care has to be

taken when processing timer-dependent data such

as the step duration for regulation or demagnetiza-

tion.

For example if an overflow occurs when calculat-

ing

software

end

demagnetization

(MCOMP+demagnetisation_time>FFh), the value

that stored in MDREG will be:

7Fh+(MCOMP+demagnetization_time-FFh)/2.

Note on commutation interrupts: It is good prac-

tice to modify the configuration for the next step as

soon as possible, i.e within the commutation inter-

rupt routine.

All registers that need to be changed at each step

have a preload register that enables the modifica-

tions for a complete new configuration to be per-

formed at the same time (at C event in normal

mode or when writing the MPHST register in direct

access mode).

These configuration bits are:

CPB, HDM, SDM and OS2 in the MCRB register

and IS[1:0], OO[5:0] in the MPHST register.

Note on initializing the MTC: As shown in Table

21 all the MTIM timer registers are in read-write

mode until the MTC clock is enabled (with the

MOE and DAC bits). This allows the timer, prescal-

er and compare registers to be properly initialized

for start-up.

In sensorless mode, the motor has to be started in

switched mode until a BEMF voltage is present on

the inputs. This means the prescaler ST[3:0] bits

and MCOMP register have to be modified by soft-

ware. When running the ST[3:0] bits can only be

incremented/decremented, so the initial value is

very important.

When starting directly in autoswitched mode (in

sensor mode for example), write an appropriate

value in the MZREG and MZPRV register to per-

form a step calculation as soon as the clock is en-

abled.

Name

Reset Value

Contents

MTIM

00h

Timer Value

MZPRV

00h

Capture Zn-1

MZREG

00h

Capture Zn

MCOMP

00h

Compare Cn+1

MDREG

00h

Demagnetization Dn

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