Datasheet

160
7593L–AVR–09/12
AT90USB64/128
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
16-8.
16.8.3 TCNT2 – Timer/Counter Register
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.
16.8.4 OCR2A – Output Compare Register A
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.
16.8.5 OCR2B – Output Compare Register B
The Output Compare Register B 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 OC2B pin.
Table 16-8. Clock Select bit description.
CS22 CS21 CS20 Description
0 0 0 No clock source (Timer/Counter stopped)
001clk
T2S
/(no prescaling)
010clk
T2S
/8 (from prescaler)
011clk
T2S
/32 (from prescaler)
100clk
T2S
/64 (from prescaler)
101clk
T2S
/128 (from prescaler)
110clk
T
2
S
/256 (from prescaler)
111clk
T
2
S
/1024 (from prescaler)
Bit 76543210
TCNT2[7:0] TCNT2
Read/write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
Bit 76543210
OCR2A[7:0] OCR2A
Read/write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
Bit 76543210
OCR2B[7:0] OCR2B
Read/write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000