UM0324 datasheet(77/105 Pages) STMICROELECTRONICS

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UM0324

Library functions

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TAC_InitTachoMeasure

TAC_GetRotorFreqInHz

Synopsis

void TAC_InitTachoMeasure(void)

Description

This function clears the software FIFO where the latest speed data

are stored. This function must be called every time the motor is started

to initialize the speed measurement process.

Input

None.

Output

None.

Functions called

TIM_ITConfig, TIM_ResetCounter, TIM_Cmd, TIM_ITConfig

Note

The first measurements following this function call are done without

filtering (the rolling average mechanism is disabled).

See also

STR750 datasheet: synchronizable standard timer.

Synopsis

u16 TAC_GetRotorFreqInHz (void)

Description

This routine returns the rotor frequency with [0.1Hz] definition. The

result is given by the following formula:

Frotor = K x (Fosc / (Capture + number of overflow x FFFF))

where K depends on the number of motor and tacho pole pairs.

Input

None.

Output

Rotor mechanical frequency, with 0.1Hz resolution, unsigned 16 bits

(direction cannot be determined using a tacho).

Functions called

GetAvrgTachoPeriod, GetLastTachoPeriod (both private functions)

Note

Result is zero if speed is too low (glitches at start for instance).

Excessive speed (or glitches) will result in a pre-defined value

returned (see Section 2.2.4 on page 21).

Maximum expectable accuracy depends on CKTIM: 60MHz will give

the best results.

Caution

This routine returns the mechanical frequency of the rotor. To find the

electrical speed, use the following conversion:

electrical frequency = mechanical frequency * number of pole pairs

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