Rainbow-electronics ATmega103L Manual de usuario descargar pdf (Pagina 38)

ATmega603/103

Timer/Counter0 Control Register - TCCR0

Timer/Counter2 Control Register - TCCR2

•

Bit 7 - Res: Reserved Bit

This bit is a reserved bit in the ATmega603/103 and always reads as zero.

•

Bit 6 - PWM0 / PWM2: Pulse Width Modulator Enable

When set (one) this bit enables PWM mode for Timer/Counter0 or Timer/Counter2. This mode is described on page 40.

•

Bits 5,4 - COM01, COM00 / COM21, COM20: Compare Output Mode, bits 1 and 0

The COMn1 and COMn0 control bits determine any output pin action following a compare match in Timer/Counter2.

Any output pin actions affect pins PB4(OC0/PWM0) or PB7(OC2/PWM2). Since this is an alternative function to an I/O

port, the corresponding direction control bit must be set (one) to control an output pin. The control configuration is shown in

Table 11.

Note: n = 0 or 2

In PWM mode, these bits have a different function. Refer to Table 14 for a detailed description.

• Bit 3 - CTC0 / CTC2: Clear Timer/Counter on Compare match

When the CTC0 or CTC2 control bit is set (one), the Timer/Counter is reset to $00 in the CPU clock cycle after a compare

match. If the control bit is cleared, the Timer continues counting and is unaffected by a compare match. Since the compare

match is detected in the CPU clock cycle following the match, this function will behave differently when a prescaling higher

than 1 is used for the timer. When a prescaling of 1 is used, and the compare register is set to C, the timer will count as fol-

lows if CTC0/2 is set:

... | C-2 | C-1 | C | 0 | 1 | ...

When the prescaler is set to divide by 8, the timer will count like this:

... | C-2, C-2, C-2, C-2, C-2, C-2, C-2, C-2 | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, 0, 0, 0, 0, 0, 0, 0, 0 | 1, 1, 1, ...

In PWM mode, this bit has no effect.

•

Bits 2,1,0 - CS02, CS01, CS00 / CS22, CS21, CS20: Clock Select bits 2,1 and 0

The Clock Select2 bits 2,1 and 0 define the prescaling source of the Timer/Counter.

Bit 7 6 5 4 3 2 1 0

33 ($53) - PWM0 COM01 COM00 CTC0 CS02 CS01 CS00 TCCR0

Read/Write R R/W R/W R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

Bit 7 6 5 4 3 2 1 0

$25 ($45) - PWM2 COM21 COM20 CTC2 CS22 CS21 CS20 TCCR2

Read/Write R R/W R/W R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

Table 11. Compare Mode Select

COMn1 COMn0 Description

0 0 Timer/Counter disconnected from output pin OCn/PWMn

0 1 Toggle the OCn/PWMn output line.

1 0 Clear the OCn/PWMn output line (to zero).

1 1 Set the OCn/PWMn output line (to one).

1 2 ... 33 34 35 36 37 38 39 40 41 42 43 ... 125 126

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Rainbow-electronics ATmega103L Manual de usuario Pagina 38

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