8-bit AVR Microcontrollers

General Timer/Counter Control 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.

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

Bit 7 – TSM: Timer/Counter Synchronization Mode

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

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

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.