ATMEGA328P-15AZ【PDF 27/83 页】MCU AVR 32K FLASH 15MHZ 32-TQFP

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PIC12(L)F1822/PIC16(L)F1823

DS41413C-page 192

2010-2012 Microchip Technology Inc.

22.1

Timer2 Operation

The clock input to the Timer2 modules is the system

instruction clock (FOSC/4).

TMR2 increments from 00h on each clock edge.

A 4-bit counter/prescaler on the clock input allows direct

input, divide-by-4 and divide-by-16 prescale options.

These options are selected by the prescaler control bits,

T2CKPS<1:0> of the T2CON register. The value of

TMR2 is compared to that of the Period register, PR2, on

each clock cycle. When the two values match, the

comparator generates a match signal as the timer

output. This signal also resets the value of TMR2 to 00h

the

cycle

and

drives

the

output

counter/postscaler

(see

Section 22.2

“Timer2

Interrupt”

The TMR2 and PR2 registers are both directly readable

and writable. The TMR2 register is cleared on any

device Reset, whereas the PR2 register initializes to

FFh. Both the prescaler and postscaler counters are

cleared on the following events:

a write to the TMR2 register

a write to the T2CON register

Power-on Reset (POR)

Brown-out Reset (BOR)

MCLR Reset

Watchdog Timer (WDT) Reset

Stack Overflow Reset

Stack Underflow Reset

RESET Instruction

22.2

Timer2 Interrupt

Timer2 can also generate an optional device interrupt.

The Timer2 output signal (TMR2-to-PR2 match)

provides the input for the 4-bit counter/postscaler. This

counter generates the TMR2 match interrupt flag which

is latched in TMR2IF of the PIR1 register. The interrupt

is enabled by setting the TMR2 Match Interrupt Enable

bit, TMR2IE of the PIE1 register.

A range of 16 postscale options (from 1:1 through 1:16

inclusive) can be selected with the postscaler control

bits, T2OUTPS<3:0>, of the T2CON register.

22.3

Timer2 Output

The unscaled output of TMR2 is available primarily to

the CCP1 module, where it is used as a time base for

operations in PWM mode.

Timer2 can be optionally used as the shift clock source

for the MSSP1 module operating in SPI mode.

Additional information is provided in Section 25.1

“Master SSP (MSSP1) Module Overview”

22.4

Timer2 Operation During Sleep

The Timer2 timers cannot be operated while the

processor is in Sleep mode. The contents of the TMR2

and PR2 registers will remain unchanged while the

processor is in Sleep mode.

Note:

TMR2 is not cleared when T2CON is

written.

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