ST7MC1K2-Auto datasheet(231/371 Pages) STMICROELECTRONICS

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On-chip peripherals

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A logic block manages capture operations depending 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 automatic mode (ECM = 0)

The clock source of the counter is selected depending on sensor type:

●

Motor control peripheral clock (16 MHz) with tachogenerator or hall sensors

●

Encoder clock

In order to optimize the accuracy of the measurement for a wide speed range, the auto-

updated prescaler functionality is used with slight modifications compared to

sensor/sensorless modes (refer to Figure 104 and Table 96).

●

When the [MTIM:MTIML] timer value reaches FFFFh, the prescaler is automatically

incremented in order to slow down the counter and avoid an overflow. To keep

consistent values, the MTIM and MTIML registers are shifted right (divided 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 better 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, that is, with a lower accuracy. No RMI interrupt 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, enabling

the capture of the maximum timer value.

The only automatically updated registers for the speed sensor mode are MTIM and MTIML.

Access to delay manager registers in speed sensor mode is summarized in Table 99.

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