Datasheet

22.9.2. TCNT0 – Timer/Counter Register
When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When
addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these offset
addresses. The device is a complex microcontroller with more peripheral units than can be supported
within the 64 location 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.
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 OCR0 Register.
Name: TCNT0
Offset: 0x24
Reset: 0x00
Property: When addressing I/O Registers as data space the offset address is 0x44
Bit 7 6 5 4 3 2 1 0
TCNT0[7:0]
Access
R/W R/W R/W R/W R/W R/W R/W R/W
Reset 0 0 0 0 0 0 0 0
Bits 7:0 – TCNT0[7:0]
Atmel ATmega64A [DATASHEET]
Atmel-8160E-ATmega64A_Datasheet_Complete-09/2015
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