Datasheet
ATmega164A/PA/324A/PA/644A/PA/1284/P
2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 113
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.
15.9.3 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.
Modifying the counter (TCNT0) while the counter is running, introduces a risk of missing a Compare Match
between TCNT0 and the OCR0x Registers.
15.9.4 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.
15.9.5 OCR0B – Output Compare Register B
The Output Compare Register B 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 OC0B pin.
15.9.6 TIMSK0 – Timer/Counter Interrupt Mask Register
• Bits 7:3 – Reserved
These bits are reserved and will always read as zero.
1 0 1 clk
I/O
/1024 (From prescaler)
1 1 0 External clock source on T0 pin. Clock on falling edge.
1 1 1 External clock source on T0 pin. Clock on rising edge.
Table 15-9. Clock Select bit description (Continued)
CS02 CS01 CS00 Description
Bit 76543210
0x26 (0x46) TCNT0[7:0] TCNT0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x27 (0x47) OCR0A[7:0] OCR0A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
0x28 (0x48) OCR0B[7:0] OCR0B
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543 2 10
(0x6E)
– – – – – OCIE0B OCIE0A TOIE0 TIMSK0
Read/Write RRRRRR/WR/WR/W
Initial Value 0 0 0 0 0 0 0 0