94
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
FOC0B bit is implemented as a strobe. Therefore it is the value present in the COM0B1:0 bits that determines the
effect of the forced compare.
A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0B as TOP.
The FOC0B bit is always read as zero.
Bits 5:4 – Res: Reserved Bits
These bits are reserved bits and will always read as zero.
Bit 3 – WGM02: Waveform Generating mode
Bits 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
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.
14.9.3
TCNT0 – 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 TCNT0 Register blocks (removes) the Compare Match on the following timer clock. Modify-
ing the counter (TCNT0) while the counter is running, introduces a risk of missing a Compare Match between
TCNT0 and the OCR0x Registers.
14.9.4
OCR0A – Output Compare Register A
The Output Compare Register A contains an 8-bit value that is continuously compared with the counter value
(TCNT0). A match can be used to generate an Output Compare interrupt, or to generate a waveform output on the
OC0A pin.
Table 14-9.
Clock Select bit description.
CS02
CS01
CS00
Description
0
No clock source (Timer/Counter stopped)
001
clkI/O/(no prescaling)
010
clkI/O/8 (from prescaler)
011
clkI/O/64 (from prescaler)
100
clkI/O/256 (from prescaler)
101
clkI/O/1024 (from prescaler)
1
0
External clock source on T0 pin. Clock on falling edge
1
External clock source on T0 pin. Clock on rising edge
Bit
76543210
TCNT0[7:0]
TCNT0
Read/write
R/W
Initial value
00000000
Bit
76543210
OCR0A[7:0]
OCR0A
Read/write
R/W
Initial value
00000000