TC0 Counter Value Register
When addressing I/O registers as data space using LD and ST instructions, the provided offset must be used. When using the I/O specific commands IN and OUT, the offset is reduced by 0x20, resulting in an I/O address offset within 0x00 - 0x3F.
The device is a complex microcontroller with more peripheral units than can be supported within the 64 locations reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60 in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.
| Bit7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| TCNT0[7:0] | |||||||
| AccessR/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W |
| Reset0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
TC0 Counter Value
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.