Datasheet

• Timer/Counter Control Register C (TCCRnC).
• Output Compare Register C, OCRnCH and OCRnCL, combined OCRnC.
The following bits are added to the 16-bit Timer/Counter Control Registers:
• COM1C1:0 are added to TCCR1A.
• FOCnA, FOCnB, and FOCnC are added in the new TCCRnC Register.
• WGMn3 is added to TCCRnB.
Interrupt flag and mask bits for output compare unit C are added.
The 16-bit Timer/Counter has improvements that will affect the compatibility in some special cases.
20.3. Accessing 16-bit Registers
The TCNTn, OCRnA/B/C, and ICRn are 16-bit registers that can be accessed by the AVR CPU via the 8-
bit data bus. A 16-bit register must be byte accessed using two read or write operations. The 16-bit timer
has a single 8-bit register for temporary storing of the High byte of the 16-bit access. The same temporary
register is shared between all 16-bit registers within the 16-bit timer. Accessing the Low byte triggers the
16-bit read or write operation. When the Low byte of a 16-bit register is written by the CPU, the High byte
stored in the temporary register, and the Low byte written are both copied into the 16-bit register in the
same clock cycle. When the Low byte of a 16-bit register is read by the CPU, the High byte of the 16-bit
register is copied into the temporary register in the same clock cycle as the Low byte is read.
Not all 16-bit accesses uses the temporary register for the High byte. Reading the OCRnA/B/C 16-bit
registers does not involve using the temporary register.
To do a 16-bit write, the High byte must be written before the Low byte. For a 16-bit read, the Low byte
must be read before the High byte.
The following code examples show how to access the 16-bit Timer Registers assuming that no interrupts
updates the temporary register. The same principle can be used directly for accessing the OCRnA/B/C
and ICRn Registers. Note that when using “C”, the compiler handles the 16-bit access.
Assembly Code Example
(1)
:.
; Set TCNTn to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNTnH,r17
out TCNTnL,r16
; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH
:.
C Code Example
(1)
unsigned int i;
:.
/* Set TCNTn to 0x01FF */
TCNTn = 0x1FF;
/* Read TCNTn into i */
i = TCNTn;
:.
Atmel ATmega64A [DATASHEET]
Atmel-8160E-ATmega64A_Datasheet_Complete-09/2015
140