ST7MC1 datasheet(173/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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MOTOR CONTROLLER (Cont’d)

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

simulated

end

demagnetization

(MCOMP+demagnetisation_time>FFh), the value

that is stored in MDREG will be:

80h+(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 41

all the MTIM timer registers are in read-write mode

until the MTC clock is enabled (with the CKE bit).

This allows the timer, prescaler and compare reg-

isters 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.

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