atmega323l ATMEL Corporation, atmega323l Datasheet - Page 58

• Manufacturer Part Number: atmega323l
• Description: Atmega323 8-bit Avr Microcontroller With 32k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Timer/Counter1 – TCNT1H
and TCNT1L
58
ATmega323(L)
When the prescaler is set to divide by 8, the timer will count like this:
... | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, C, C, C, C, C, C, C | 0, 0, 0, 0, 0, 0, 0, 0
|1,1,1,1,1,1,1,1|...
In PWM mode, this bit has a different function. If the CTC1 bit is cleared in PWM mode,
the Timer/Counter1 acts as an up/down counter. If the CTC1 bit is set (one), the
Timer/Counter wraps when it reaches the TOP value. Refer to page 60 for a detailed
description.
• Bits 2..0 – CS12, CS11, CS10: Clock Select1, Bit 2, 1, and 0
The Clock Select1 bits 2, 1, and 0 define the prescaling source of Timer/Counter1.
Table 19. Clock 1 Prescale Select
The Stop condition provides a Timer Enable/Disable function. The prescaled modes are
scaled directly from the CK Oscillator clock. If the external pin modes are used for
Timer/Counter1, transitions on PB1/(T1) will clock the counter even if the pin is config-
ured as an output. This feature can give the user SW control of the counting.
This 16-bit register contains the prescaled value of the 16-bit Timer/Counter1. To
ensure that both the high and Low Bytes are read and written simultaneously when the
CPU accesses these registers, the access is performed using an 8-bit temporary regis-
ter (TEMP). This temporary register is also used when accessing OCR1A, OCR1B, and
ICR1. If the main program and also interrupt routines perform access to registers using
TEMP, interrupts must be disabled during access from the main program and interrupt
routines.
Bit
$2D ($4D)
$2C ($4C)
Read/Write
Initial Value
CS12
0
0
0
0
1
1
1
1
MSB
R/W
R/W
15
7
0
0
CS11
0
0
1
1
0
0
1
1
R/W
R/W
14
6
0
0
CS10
0
1
0
1
0
1
0
1
R/W
R/W
13
5
0
0
Description
Stop, the Timer/Counter1 is Stopped.
CK
CK/8
CK/64
CK/256
CK/1024
External Pin T1, Falling Edge
External Pin T1, Rising Edge
R/W
R/W
12
4
0
0
R/W
R/W
11
3
0
0
R/W
R/W
10
2
0
0
R/W
R/W
9
1
0
0
LSB
R/W
R/W
1457G–AVR–09/03
8
0
0
0
TCNT1H
TCNT1L