at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 87

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

7734M–AVR–03/10
Note:
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt occurs
between the two instructions accessing the 16-bit register, and the interrupt code updates the temporary
register by accessing the same or any other of the 16-bit Timer Registers, then the result of the access out-
side the interrupt will be corrupted. Therefore, when both the main code and the interrupt code update the
temporary register, the main code must disable the interrupts during the 16-bit access.
The following code examples show how to do an atomic read of the TCNT1 Register contents. Reading
any of the OCR1A/B or ICR1 Registers can be done by using the same principle.
Assembly Code Examples
C Code Examples
Assembly Code Example
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT1H,r17
out TCNT1L,r16
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
...
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1 = 0x1FF;
/* Read TCNT1 into i */
i = TCNT1;
...
1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS” and
“STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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AT90PWM81
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