Datasheet

20.4.1 General Timer/Counter Control Register

Name: GTCCR

Offset: 0x43

Reset: 0x00

Property: When addressing as I/O register: address offset is 0x23

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.

Bit 7 6 5 4 3 2 1 0

TSM PSRASY PSRSYNC

Access

R/W R/W R/W

Reset 0 0 0

Bit 7 – TSM Timer/Counter Synchronization Mode

Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the value

that is written to the PSRASY and PSRSYNC bits is kept, hence keeping the corresponding prescaler

reset signals asserted. This ensures that the corresponding Timer/Counters are halted and can be

configured to the same value without the risk of one of them advancing during configuration. When the

TSM bit is written to zero, the PSRASY and PSRSYNC bits are cleared by hardware, and the Timer/

Counters start counting simultaneously.

Bit 1 – PSRASY Prescaler Reset Timer/Counter2

When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally cleared immediately

by hardware. If the bit is written when Timer/Counter2 is operating in Asynchronous mode, the bit will

remain one until the prescaler has been reset. The bit will not be cleared by hardware if the TSM bit is

set.

Bit 0 – PSRSYNC Prescaler Reset

When this bit is one, Timer/Counter 0, 1, 3, 4 prescaler will be Reset. This bit is normally cleared

immediately by hardware, except if the TSM bit is set. Note that Timer/Counter 0, 1, 3, 4 share the same

prescaler and a reset of this prescaler will affect the mentioned timers.

ATmega328PB

Timer/Counter 0, 1, 3, 4 Prescalers

Datasheet Complete

DS40001906C-page 217