AT90USB64/128
• Bit 3 – WGM22: Waveform Generation Mode
See the description in the “Timer/Counter Control Register A – TCCR2A” on page 161.
• Bit 2:0 – CS22:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Table
15-8.
Table 15-8. Clock Select Bit Description
CS22
CS21
CS20
Description
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
No clock source (Timer/Counter stopped).
clkT2S/(No prescaling)
clkT2S/8 (From prescaler)
clkT2S/32 (From prescaler)
clkT2S/64 (From prescaler)
clkT2S/128 (From prescaler)
clkT S/256 (From prescaler)
2
clkT S/1024 (From prescaler)
2
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
15.8.3
Timer/Counter Register – TCNT2
Bit
7
6
5
4
3
2
1
0
TCNT2[7:0]
TCNT2
Read/Write
Initial Value
R/W
0
R/W
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT2 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT2) while the counter is running,
introduces a risk of missing a Compare Match between TCNT2 and the OCR2x Registers.
15.8.4
Output Compare Register A – OCR2A
Bit
7
6
5
4
3
2
1
0
OCR2A[7:0]
OCR2A
Read/Write
Initial Value
R/W
0
R/W
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
The Output Compare Register A contains an 8-bit value that is continuously compared with the
counter value (TCNT2). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC2A pin.
15.8.5
Output Compare Register B – OCR2B
Bit
7
6
5
4
3
2
1
0
OCR2B[7:0]
OCR2B
Read/Write
Initial Value
R/W
0
R/W
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
165
7593A–AVR–02/06
ATMEL [ ATMEL ]
