ATA5771 ATMEL Corporation, ATA5771 Datasheet - Page 140

• Manufacturer Part Number: ATA5771
• Manufacturer: ATMEL Corporation

12.2.3
12.3
88
Accessing 16-bit Registers
ATtiny24/44/84
Compatibility
The 16-bit Timer/Counter has been updated and improved from previous versions of the 16-bit
AVR Timer/Counter. This 16-bit Timer/Counter is fully compatible with the earlier version
regarding:
The following control bits have changed name, but have same functionality and register location:
The following bits are added to the 16-bit Timer/Counter Control Registers:
The 16-bit Timer/Counter has improvements that will affect the compatibility in some special
cases.
The TCNT1, OCR1A/B, and ICR1 are 16-bit registers that can be accessed by the AVR CPU via
the 8-bit data bus. The 16-bit register must be byte accessed using two read or write operations.
Each 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 each 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 tempo-
rary 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 OCR1A/B 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 OCR1A/B and ICR1 Registers. Note that when using “C”, the compiler handles the 16-bit
access.
• All 16-bit Timer/Counter related I/O Register address locations, including Timer Interrupt
• Bit locations inside all 16-bit Timer/Counter Registers, including Timer Interrupt Registers.
• Interrupt Vectors.
• PWM10 is changed to WGM10.
• PWM11 is changed to WGM11.
• CTC1 is changed to WGM12.
• 1A and 1B are added to TCCR1A.
• WGM13 is added to TCCR1B.
Registers.
8006G–AVR–01/08