STV3550 datasheet(92/144 Pages) STMICROELECTRONICS

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STV3550

7.5

Basic Timer

The chip embeds four Basic Timers. Each timer includes a programmable 16-bit down counter and

an associated 16-bit prescaler with Single and Continuous counting modes capability. The input

clock to the prescaler can be driven either by an internal clock equal (27 MHz) divided by 4 or by an

external clock connected to the Timer Input pin. The maximum input clock frequency cannot exceed

the internal clock frequency divided by 8. The input and output pins, when available, may be

connected as Alternate Functions of an I/O port bit.

The Basic Timer can be used in one of four programmable input modes:

●

event counter,

●

gated external input mode,

●

triggerable input mode,

●

retriggerable input mode.

The Timer Output pin can be used to generate a Square Wave or Pulse Width Modulated signal.

The Basic Timer End Of Count condition is able to generate an interrupt. The End of Count

condition is defined as the Counter Underflow, whenever 00h is reached.

7.5.1

Functional Description

7.5.1.1 Timer/Counter Control

The timer can run in Continuous or Single mode. An initial pre-scale or counter value can be loaded.

IMPORTANT: In order to prevent incorrect counting of the Basic Timer, the prescaler and counter

registers must be initialized before the timer is started. If this is not done, the counting will start with

the reset values.

Single/Continuous Mode

In Single mode, at the End of Count, the Basic Timer stops, reloads the constant and resets the

Start/Stop bit. (The user programmer can inspect the current timer status by reading this bit). Setting

the Start/Stop bit will restart the counter.

In Continuous mode, at the End of the Count, the counter automatically reloads the constant and

restarts. It is only stopped by resetting the Start/Stop bit.

Figure 58: Basic Timer Block Diagram

Timer Output

INEN INMD1 INMD0

BTimerPres

16-bit Prescaler

OUTMD1

OUTMD0

Output Control Logic

End of Count

Interrupt

Timer Input

Internal Clock: 4

BTimerCVL

16-bit Downcounter

Basic

Timer

Clock

Input &

Clock Control Logic

MUX

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