ATMEGA8L ATMEL [ATMEL Corporation], ATMEGA8L Datasheet - Page 121

• Manufacturer Part Number: ATMEGA8L
• Description: 8-bit AVR with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Timer/Counter Prescaler
Special Function IO Register –
SFIOR
2486M–AVR–12/03
Figure 56. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named clk
the main system I/O clock clk
asynchronously clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a
Real Time Counter (RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected
from Port B. A crystal can then be connected between the TOSC1 and TOSC2 pins to
serve as an independent clock source for Timer/Counter2. The Oscillator is optimized
for use with a 32.768 kHz crystal. Applying an external clock source to TOSC1 is not
recommended.
For Timer/Counter2, the possible prescaled selections are: clk
clk
selected. Setting the PSR2 bit in SFIOR resets the prescaler. This allows the user to
operate with a predictable prescaler.
• Bit 1 – PSR2: Prescaler Reset Timer/Counter2
When this bit is written to one, the Timer/Counter2 prescaler will be reset. The bit will be
cleared by hardware after the operation is performed. Writing a zero to this bit will have
no effect. This bit will always be read as zero if Timer/Counter2 is clocked by the internal
CPU clock. If this bit is written when Timer/Counter2 is operating in Asynchronous
mode, the bit will remain one until the prescaler has been reset.
Bit
Read/Write
Initial Value
T2S
/128, clk
TOSC1
clk
PSR2
CS20
CS21
CS22
AS2
I/O
T2S
7
–
R
0
/256, and clk
R
6
–
0
clk
T2S
T2S
I/O
R
5
–
0
. By setting the AS2 bit in ASSR, Timer/Counter2 is
/1024. Additionally, clk
TIMER/COUNTER2 CLOCK SOURCE
Clear
R
4
–
0
0
ACME
10-BIT T/C PRESCALER
R/W
3
0
T2S
clk
T2
. clk
T2S
PUD
R/W
T2S
2
0
as well as 0 (stop) may be
is by default connected to
T2S
ATmega8(L)
PSR2
/8, clk
R/W
1
0
T2S
PSR10
R/W
/32, clk
0
0
SFIOR
T2S
/64,
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