164
7679H–CAN–08/08
AT90CAN32/64/128
Figure 14-14.
Timer/Counter2 Crystal Oscillator Connections
A external clock can also be used using TOSC1 as input. Setting AS2 and EXCLK enables this
configuration.
Figure 14-15.
Timer/Counter2 External Clock Connections
For Timer/Counter2, the possible prescaled selections are: clk
T2S
/8, clk
T2S
/32, clk
T2S
/64,
clk
T2S
/128, clk
T2S
/256, and clk
T2S
/1024. Additionally, clk
T2S
as well as 0 (stop) may be selected.
Setting the PSR2 bit in GTCCR resets the prescaler. This allows the user to operate with a pre-
dictable prescaler.
14.11.1
General Timer/Counter Control Register – GTCCR
• 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 Syn-
for a description of the Timer/Counter Synchronization mode.
TOSC2
TOSC1
GND
12 - 22 pF
12 - 22 pF
32.768 KHz
TOSC2
TOSC1
NC
External
Clock
Signal
Bit
7
6
5
4
3
2
1
0
TSM
–
–
–
–
–
PSR2
PSR310
GTCCR
Read/Write
R/W
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
