ST52F510 datasheet(72/106 Pages) STMICROELECTRONICS

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ST52F510/F513/F514

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Figure 12.2 Timer 0 External Start/Stop Mode

TxSTRT

signal

starts/stops

the

Timer

from

counting only if the peripherals are configured in

Timer mode. The Timers are started by writing 1 in

the TXSTRT bit of the PWMx_CR1 and are

stopped by writing 0. This signal can be generated

internally and/or externally by forcing the TSTRT

pin (only TIMER0).

TIMER 0 START/STOP can be given externally on

the TSTRT pin. In this case, the T0STRT signal

allows the user to work in two different configurable

modes (see Figure 12.2):

LEVEL (Time Counter): If the T0STRT signal is

high, the Timer starts counting. When the

T0STRT is low the timer stops counting and the

16-bit current value is stored in the

PWM0_COUNT_IN_x Input Registers couple.

EDGE (Period Counter): After reset, on the first

T0STRT rising edge, TIMER 0 starts counting

and at the next rising edge it stops. In this

manner the period of an external signal may be

measured.

The same above mentioned modes, can be used

to reset the Timer0 by using the TRES pin signal.

The polarity of the T0SRTR Start/Stop signal can

be changed by setting the STRPOL and RESPOL

bits in the INT_POL Configuration Register (01h bit

3 and 4). When these bits are set, the PWM/Timer

0 is Started/Set on the low level or in the falling

edge of the signal applied in the pins.

The Timer output signal, TxOUT, is a signal with a

frequency equal to the one of the 16 bit-Prescaler

output signal, PRESCOUTx, divided by a 16-bit

counter set by writing the Output Register couple

PWMx_COUNT_OUT_x.

Note: the contents of these registers upgrades the

Timer counter after it stops counting. Since the

cause side effects. In order to avoid this, the user

should write the MSB before writing the LSB:

actually, the 16-bit value is latched in parallel when

the LSB is written. By writing only the LSB (and

MSB equal to 0), the PWM/Timer is used as with

an 8 bit counter.

Warning: in Timer Mode the Reload Register

couple PWMx_RELOAD_x (see PWM mode) must

be set to the higher value FFFFh (65535)

otherwise it can affect the count duration.

There can be two types of TxOUT waveforms:

type 1: TxOUT waveform equal to a square

wave with a 50% duty-cycle

type 2: TxOUT waveform equal to a pulse signal

with the pulse duration equal to the Prescaler

output signal.

Figure 12.3 TxOUT Signal Types

Level

Ed ge

sta rt

sto p

start

stop

start

Reset

Clock

Cou nted

Va lue

Timer Output

Type 1

Type 2

Prescout*Counter

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