ATMEGA169 ATMEL [ATMEL Corporation], ATMEGA169 Datasheet - Page 142

• Manufacturer Part Number: ATMEGA169
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Timer/Counter Prescaler
General Timer/Counter
Control Register – GTCCR
142
ATmega169/V
Figure 64. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named clk
the main system I/O clock clk
chronously 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 C. 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. If applying an external clock on TOSC1, the EXCLK bit in
ASSR must be set.
For Timer/Counter2, the possible prescaled selections are: clk
clk
selected. Setting the PSR2 bit in GTCCR resets the prescaler. This allows the user to
operate with a predictable prescaler.
• Bit 1 – PSR2: Prescaler Reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally
cleared immediately by hardware. If the bit is written when Timer/Counter2 is operating
in asynchronous mode, the bit will remain one until the prescaler has been reset. The bit
will not be cleared by hardware if the TSM bit is set. Refer to the description of the “Bit 7
– TSM: Timer/Counter Synchronization Mode” on page 94 for a description of the
Timer/Counter Synchronization mode.
Bit
Read/Write
Initial Value
TOSC1
T2S
clk
PSR2
CS20
CS21
CS22
AS2
/128, clk
I/O
TSM
R/W
T2S
7
0
/256, and clk
R
6
–
0
clk
T2S
IO
T2S
. By setting the AS2 bit in ASSR, Timer/Counter2 is asyn-
R
5
–
0
Clear
/1024. Additionally, clk
TIMER/COUNTER2 CLOCK SOURCE
R
4
–
0
0
10-BIT T/C PRESCALER
R
3
–
0
T2S
clk
. clk
T2
T2S
T2S
R
2
–
0
as well as 0 (stop) may be
is by default connected to
T2S
PSR2
/8, clk
R/W
1
0
T2S
PSR10
R/W
/32, clk
2514P–AVR–07/06
0
0
GTCCR
T2S
/64,