ST62T40B datasheet(39/72 Pages) STMICROELECTRONICS

39 / 72 page

39/72

ST62T40B/E40B

4.2 TIMER 1 & 2

The MCU features two on-chip Timer peripheral

named TIMER 1 & TIMER 2. Each of these timers

consist of an 8-bit counter with a 7-bit programma-

ble prescaler, giving a maximum count of 215.

Figure 22 and Figure 23 show the Timer Block Di-

agrams. An external TIMER pin is available to the

user on the TIMER 1 allowing external control of

the counting clock or signal generation.

The content of the 8-bit counter can be read/writ-

ten in the Timer/Counter register, TCR, while the

state of the 7-bit prescaler can be read in the PSC

the TSCR register as described in the following

paragraphs.

The 8-bit counter is decremented by the output

(rising edge) coming from the 7-bit prescaler and

can be loaded and read under program control.

When it decrements to zero then the TMZ (Timer

Zero) bit in the TSCR is set to “1”. If the ETI (Ena-

ble Timer Interrupt) bit in the TSCR is also set to

“1”, an interrupt request is generated as described

in the Interrupt Chapter. The Timer interrupt can

be used to exit the MCU from WAIT mode.

The prescaler input can be either the internal fre-

quency fINT divided by 12 (TIMER 1 & 2) or an ex-

ternal clock applied to the TIMER pin (TIMER 1).

The prescaler decrements on the rising edge. De-

pending on the division factor programmed by

PS2, PS1 and PS0 bits in the TSCR. The clock in-

put of the timer/counter register is multiplexed to

different sources. For division factor 1, the clock

input of the prescaler is also that of timer/counter;

for factor 2, bit 0 of the prescaler register is con-

nected to the clock input of TCR. This bit changes

its state at half the frequency of the prescaler input

clock. For factor 4, bit 1 of the PSC is connected to

the clock input of TCR, and so forth. The prescaler

initialize bit, PSI, in the TSCR register must be set

to “1” to allow the prescaler (and hence the coun-

ter) to start. If it is cleared to “0”, all the prescaler

bits are set to “1” and the counter is inhibited from

counting. The prescaler can be loaded with any

value between 0 and 7Fh, if bit PSI is set to “1”.

The prescaler tap is selected by means of the

PS2/PS1/PS0 bits in the control register.

Figure 21 illustrates the Timer’s working principle.

Figure 21. Timer Working Principle

BIT0

BIT1

BIT2

BIT3

BIT6

BIT5

BIT4

CLOCK

7-BIT PRESCALER

8-1 MULTIPLEXER

8-BIT COUNTER

BIT0

BIT1

BIT2

BIT3

BIT4

BIT5

BIT6

BIT7

PS0

PS1

PS2

VA00186

ST62T40B Datasheet(PDF) 39 Page - STMicroelectronics

ST62T40B Datasheet(HTML) 39 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

Datasheet Download

Link URL