ST7MC2N6T3 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST7MC2N6T3

8-bit MCU with nested interrupts, Flash, 10-bit ADC, brushless motor control, five timers, SPI, LINSCI™

STMicroelectronics 

ST7MC1xx/ST7MC2xx

MOTOR CONTROLLER (Cont’d)

10.6.7.5 Speed Measurement Mode

Motor speed can be measured using two methods

depending on sensor type: period measurement or

pulse counting. Typical sensor handling is de-

scribed here.

Incremental encoders allows accurate speed

measurement by providing a large number of puls-

es per revolution (ppr) with ppr rates up to several

thousands; the higher the ppr rate, the higher the

resolution. The proposed method consists of

counting the number of clock cycles issued by the

Incremental Encoder Interface (Encoder Clock)

during a fixed time window (refer to Figure 100).

The tachogenerator has a much lower ppr rate

than the encoder (typically factor 10). In this con-

text, it is more meaningful to measure the period

between Tacho Captures (i.e. relevant transitions

of the incoming signals). Accuracy is imposed by

the reference clock, i.e. the CPU clock (refer to

Figure 99).

Figure 99. Tachogenerator period acquisition using MTIM timer

Decreasing Speed

Comparator

Output

Tacho

Capture

Compare

Value

MTIM Counter

S

Value

Interrupts

CC

C

C

C

C

C

C

To interrupt generator

(Capture Event)

S

To interrupt generator

(Speed Error Event)

Figure 100. Encoder Clock frequency measure using MTIM timer

Decreasing Speed

Encoder

Clock

Capture

(triggered by software

or Real-time Clock)

MTIM Counter

Value

Interrupts

C

C

C

C

C

C

C

C

To interrupt generator

(Capture Event)

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