ATmega644A Atmel Corporation, ATmega644A Datasheet - Page 203
ATmega644A
Manufacturer Part Number
ATmega644A
Description
Manufacturer
Atmel Corporation
Specifications of ATmega644A
Flash (kbytes)
64 Kbytes
Pin Count
44
Max. Operating Frequency
20 MHz
Cpu
8-bit AVR
# Of Touch Channels
16
Hardware Qtouch Acquisition
No
Max I/o Pins
32
Ext Interrupts
32
Usb Speed
No
Usb Interface
No
Spi
3
Twi (i2c)
1
Uart
2
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
8
Adc Resolution (bits)
10
Adc Speed (ksps)
15
Analog Comparators
1
Resistive Touch Screen
No
Temp. Sensor
No
Crypto Engine
No
Sram (kbytes)
4
Eeprom (bytes)
2048
Self Program Memory
YES
Dram Memory
No
Nand Interface
No
Picopower
No
Temp. Range (deg C)
-40 to 85
I/o Supply Class
1.8 to 5.5
Operating Voltage (vcc)
1.8 to 5.5
Fpu
No
Mpu / Mmu
no / no
Timers
3
Output Compare Channels
6
Input Capture Channels
1
Pwm Channels
6
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
ATmega644A-AU
Manufacturer:
Atmel
Quantity:
135
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20.5.1
8272C–AVR–06/11
USART MSPIM Initialization
The UDORDn bit in UCSRnC sets the frame format used by the USART in MSPIM mode. The
Receiver and Transmitter use the same setting. Note that changing the setting of any of these
bits will corrupt all ongoing communication for both the Receiver and Transmitter.
16-bit data transfer can be achieved by writing two data bytes to UDRn. A UART transmit com-
plete interrupt will then signal that the 16-bit value has been shifted out.
The USART in MSPIM mode has to be initialized before any communication can take place. The
initialization process normally consists of setting the baud rate, setting master mode of operation
(by setting DDR_XCKn to one), setting frame format and enabling the Transmitter and the
Receiver. Only the transmitter can operate independently. For interrupt driven USART opera-
tion, the Global Interrupt Flag should be cleared (and thus interrupts globally disabled) when
doing the initialization.
Note:
Before doing a re-initialization with changed baud rate, data mode, or frame format, be sure that
there is no ongoing transmissions during the period the registers are changed. The TXCn Flag
can be used to check that the Transmitter has completed all transfers, and the RXCn Flag can
be used to check that there are no unread data in the receive buffer. Note that the TXCn Flag
must be cleared before each transmission (before UDRn is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C func-
tion that are equal in functionality. The examples assume polling (no interrupts enabled). The
baud rate is given as a function parameter. For the assembly code, the baud rate parameter is
assumed to be stored in the r17:r16 registers.
To ensure immediate initialization of the XCKn output the baud-rate register (UBRRn) must be
zero at the time the transmitter is enabled. Contrary to the normal mode USART operation the
UBRRn must then be written to the desired value after the transmitter is enabled, but before the
first transmission is started. Setting UBRRn to zero before enabling the transmitter is not neces-
sary if the initialization is done immediately after a reset since UBRRn is reset to zero.
ATmega164A/PA/324A/PA/644A/PA/1284/P
203
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