ST7MC1 datasheet(180/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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MOTOR CONTROLLER (Cont’d)

Hall sensors (or equivalent sensors providing posi-

tion information) are widely used for motor control.

There are two cases to be considered:

– BLDC motor or six-step synchronous motor

drive; “Sensor Mode” is recommended in this

case, as most tasks are performed by hardware

in the Delay Manager

– BLAC, asynchronous or motors supplied with 3-

phase sinewave-modulated PWM signals in gen-

eral; in this case “Speed Sensor Mode” allows

high accuracy speed measurement (the Sensor

Mode of the Delay Manager being unsuitable for

sinewave generation). Position information is

handled by software to lock the statoric field to

the rotoric one for driving synchronous motors.

Hall sensors are usually arranged in a 120° config-

uration. In that case they provide 3 ppr with both

rising and falling edge triggering; the tachogenera-

tor measurement method can therefore be ap-

plied. The main difference lies in the fact that one

must use the position information they provide.

This can be done using the three MCIx pins and

the analog multiplexer to know which of the 3 sen-

sors toggled; an interrupt is generated just after

the expected transition (refer to Figure 101).

As described in Figure 102, the MTIM Timer is re-

configured depending on the selected sensor. This

means that most of Delay Manager registers are

used for a different purpose, with modified func-

tionalities.

For greater precision, the MTIM Up-counter is ex-

tended to 16 bits using MTIM and an additional

MTIML register. On a capture event, the current

counter value is captured and the counter

[MTIM:MTIML] is cleared. The counting direction

is not affected by the EDIR bit when using an en-

coder sensor.

A 16-bit capture register is used to store the cap-

tured value of the extended MTIM counter: the

speed result will be either a period in clock cycles

or a number of encoder pulses. This 16-bit register

is mapped in the MZREG and MZPRV register ad-

dresses. To ensure that the read value is not cor-

rupted between the high and low byte accesses, a

read access to the MSB of this register (MZREG)

locks the LSB (ie MZPRV content is locked) until it

is read and any other capture event in between

these two accesses is discarded.

A compare unit allows a maximum value to be en-

tered for the tacho periods. If the 16-bit counter

[MTIM:MTIML] exceeds this value, a Speed Error

interrupt is generated. This may be used to warn

the user that the tachogenerator signal is lost

(wires disconnected, motor stalled,...). As 8-bit ac-

curacy is sufficient for this purpose, only the MS-

Byte of the counter (i.e. MTIM) is compared to 8-bit

compare register, mapped in the MDREG register

location. The LSByte is nevertheless compared

with a fixed FFh value. Available values for com-

parison are therefore FFFFh, FEFFh, FDFFh, ...,

01FFh, 00FFh.

Note: This functionality is not useful when using

an encoder. With an encoder, user must monitor

the captured values by software during the period-

ic capture interrupts: for instance, when driving an

AC motor, if the values are too low compared to

the stator frequency, a software interrupt may be

triggered.

Figure 101. Hall sensor period acquisition using MTIM timer

1 mechanical cycle

MCIA: Hall Sensor 1

MCIB: Hall Sensor 2

MCIC: Hall Sensor 3

Tacho Capture

Period measurements

Interrupts

1-2

3-1

2-3

3-1

1-2

2-3

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