STV3550 datasheet(93/144 Pages) STMICROELECTRONICS

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STV3550

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7.5.1.2 Basic Timer Input Modes

Several inputs modes are available for the basic timers.

●

Event Counter Mode

The Basic Timer is driven by the signal applied to the input pin (Input Timer) which acts as an

external clock. In this case, the unit works as an event counter. The event is a high to low

transition on Input Timer. Spacing between trailing edges should be at least one internal clock

cycle multiplied by 8 (i.e. the maximum Basic Timer input frequency is 3.38 MHz when the

internal clock frequency is 27 MHz).

●

Gated Input Mode

The Basic Timer uses the internal clock and starts and stops the Timer according to the state of

Input Timer pin. When the status of the Input Timer pin is High, the Basic Timer count operation

proceeds. When the status of the Input Timer pin is Low, the counting is stopped.

●

Triggerable Input Mode

The Basic Timer is triggered only once by:

➢ enabling the timer,

➢ a high to low transition on the Input Timer pin.

The timer must be reactivated once the counter reaches 0.

●

Retriggerable Input Mode

In this mode, each high to low transition on the Input Timer pin causes the counter to restart

from the last constant loaded in the prescaler and load registers.

As with Triggerable Input Mode, the Basic Timer is started by:

➢ enabling the timer,

➢ a high to low transition on the Input Timer pin.

7.5.1.3 Basic Timer Output Modes

Several output modes are available for the basic timers.

●

No Output Mode

The output is disabled and the corresponding pin is set high (reset state).

●

Square Wave Output Mode

The Basic Timer toggles the state of the Output Timer pin on every End Of Count condition.

When the internal clock frequency is 27 MHz, square waves can be generated within a period

ranging from 296 ns to 1271 seconds.

●

PWM Output Mode

The output value can be forced to high or low when the timer reaches End Of Count. This

enables the user to generate PWM signals by modifying the value previously forced between

End of Count events, based on software counters decremented on Basic Timer interrupts.

7.5.2

Interrupt Selection

The Basic Timer can generate an interrupt request at every End of Count event.

Note:

If the counter is loaded with the value 0000h, the counting is stopped but the interrupt is

continuously generated.

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