AT90USB1286-16MU ATMEL [ATMEL Corporation], AT90USB1286-16MU Datasheet - Page 170

• Manufacturer Part Number: AT90USB1286-16MU
• Description: Microcontroller with 64/128K Bytes of ISP Flash and USB Controller
• Manufacturer: ATMEL [ATMEL Corporation]

15.10 Timer/Counter Prescaler
15.10.1
170
AT90USB64/128
General Timer/Counter Control Register – GTCCR
Figure 15-12. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named clk
system I/O clock clk
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. Apply-
ing an external clock source to TOSC1 is not recommended.
For Timer/Counter2, the possible prescaled selections are: clk
clk
Setting the PSRASY bit in GTCCR resets the prescaler. This allows the user to operate with a
predictable prescaler.
• Bit 1 – PSRASY: 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
Register – GTCCR” on page 100
Bit
Read/Write
Initial Value
T2S
/128, clk
PSRASY
TOSC1
clk
CS20
CS21
CS22
AS2
I/O
7
TSM
R/W
0
T2S
/256, and clk
6
–
R
0
IO
. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously
clk
5
–
R
0
T2S
T2S
/1024. Additionally, clk
for a description of the Timer/Counter Synchronization mode.
Clear
4
–
R
0
TIMER/COUNTER2 CLOCK SOURCE
3
–
R
0
T2S
0
. clk
10-BIT T/C PRESCALER
T2S
2
–
R
0
T2S
clk
as well as 0 (stop) may be selected.
T2
is by default connected to the main
“General Timer/Counter Control
1
PSRA-
SY
R/W
0
T2S
/8, clk
0
PSRSY
NC
R/W
0
T2S
/32, clk
GTCCR
7593A–AVR–02/06
T2S
/64,