TC3 Counter Value Low and High byte
The TCNT3L and TCNT3H register pair represents the 16-bit value, TCNT3. The low byte [7:0] (suffix L) is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset + 0x01. For more details on reading and writing 16-bit registers, refer to Accessing 16-bit Timer/Counter Registers.
| Bit15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 |
| TCNT3[15:8] | |||||||
| AccessR/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W |
| Reset0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Bit7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| TCNT3[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 |
Timer/Counter 3 Counter Value
The two Timer/Counter I/O locations (TCNT3H and TCNT3L, combined TCNT3) give direct access, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes are read and written simultaneously when the CPU accesses these registers, the access is performed using an 8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit registers. Refer to Accessing 16-bit Timer/Counter Registers for details.
Modifying the counter (TCNT3) while the counter is running introduces a risk of missing a compare match between TCNT3 and one of the OCR3x Registers.
Writing to the TCNT3 Register blocks (removes) the compare match on the following timer clock for all compare units.