ATmega406 Atmel Corporation, ATmega406 Datasheet - Page 96

• Manufacturer Part Number: ATmega406
• Manufacturer: Atmel Corporation

Specifications of ATmega406

• Flash (kbytes): 40 Kbytes
• Pin Count: 48
• Max. Operating Frequency: 1 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 8
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 18
• Ext Interrupts: 4
• Usb Speed: No
• Usb Interface: No
• Twi (i2c): 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 11
• Adc Resolution (bits): 12
• Adc Speed (ksps): 1.9
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 2
• Eeprom (bytes): 512
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -30 to 85
• I/o Supply Class: 4.0 to 25
• Operating Voltage (vcc): 4.0 to 25
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 3
• Pwm Channels: 2
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

16.2
96
Accessing 16-bit Registers
ATmega406
The Output Compare Register (OCR1A) is compared with the Timer/Counter value at all time.
The compare match event will set the Compare Match Flag (OCF1A) which can be used to gen-
erate an output compare interrupt request.
The TCNT1 and OCR1A 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 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 OCR1A 16-bit
register 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 Register. Note that when using “C”, the compiler handles the 16-bit access.
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
Assembly Code Examples
C Code Examples
...
; 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. See
”About Code Examples” on page
(1)
(1)
7.
2548E–AVR–07/06