ST7MC1 datasheet(182/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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MOTOR CONTROLLER (Cont’d)

A logic block manages capture operations de-

pending on the sensor type. A capture is initiated

on an active edge (“Tacho capture” event) when

using a tachogenerator.

If an encoder is used, the capture is triggered on

two events depending on the Encoder Capture

Mode bit (ECM) in the MZFR register:

– Reading the MSB of the counter in manual

mode (ECM = 1)

– Interrupt from the Real Time Clock in automat-

ic mode (ECM = 0)

The clock source of the counter is selected de-

pending on sensor type:

– Motor Control Peripheral clock (16 MHz) with

tachogenerator or Hall sensors

– Encoder Clock

In order to optimize the accuracy of the measure-

ment for a wide speed range, the auto-updated

prescaler functionality is used with slight modifica-

tions compared to Sensor/Sensorless Modes (re-

fer to Figure 103 and Table 38).

– When the [MTIM:MTIML] timer value reaches

FFFFh, the prescaler is automatically increment-

ed in order to slow down the counter and avoid

an overflow. To keep consistent values, the

MTIM and MTIML registers are shifted right (di-

vided by two). The RPI bit in the MISR register is

set and an interrupt is generated (if RIM is set).

– When a capture event occurs, if the

[MTIM:MTIML] timer value is below 5500h, the

prescaler is automatically decremented in order

to speed up the counter and keep precision bet-

ter than 0.005% (1/5500h). The MTIM and

MTIML registers are shifted left (multiplied by

two). The RMI bit in the MISR register is set and

an interrupt is generated if RIM is set.

– If the prescaler contents reach the value 0, it can

no longer be automatically decremented, the

[MTIM:MTIML] timer continues working with the

same prescaler value, i.e. with a lower accuracy.

No RMI interrrupt can be generated.

– If the prescaler contents reach the value 15, it

can no longer be automatically incremented.

When the timer reaches the value FFFFh, the

prescaler and all the relevant registers remain

unchanged and no interrupt is generated, the

timer clock is disabled, and its contents stay at

FFFFh. The capture logic block still works, ena-

bling the capture of the maximum timer value.

The only automatically updated registers for the

Speed Sensor Mode are MTIM and MTIML. Ac-

cess to Delay manager registers in Speed Sensor

Mode is summarised in Table 41.

Figure 103. Auto-updated prescaler functional diagram

Ratio > 0?

Ratio = Ratio - 1

Counter = 0

Begin

End

Yes

Capture with [MTIM:MTIML] Timer < 5500h

Ratio < Fh?

Ratio = Ratio + 1

Counter = Counter/2

Begin

End

Yes

[MTIM:MTIML] Timer Overflow

Slow-down control

Speed-up control

(MTIM = MTIML = FFh)

(MZREG < 55h)

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