ATMEGA644P-20PQ Atmel, ATMEGA644P-20PQ Datasheet - Page 193

• Manufacturer Part Number: ATMEGA644P-20PQ
• Description: MCU AVR 64K FLASH 20MHZ 40-PDIP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA644P-20PQ

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 64KB (32K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 2K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 40-DIP (0.600", 15.24mm)
• For Use With: ATSTK600 - DEV KIT FOR AVR/AVR32
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

16.11.5
8011O–AVR–07/10
UBRRnL and UBRRnH – USART Baud Rate Registers
• Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode is
used. The UCPOLn bit sets the relationship between data output change and data input sample,
and the synchronous clock (XCKn).
Table 16-8.
• Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit must be
written to zero when UBRRH is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the four
most significant bits, and the UBRRL contains the eight least significant bits of the USART baud
rate. Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud rate is
changed. Writing UBRRL will trigger an immediate update of the baud rate prescaler.
Bit
Read/Write
Initial Value
UCPOLn
0
1
UCPOLn Bit Settings
Transmitted Data Changed (Output of
TxDn Pin)
Rising XCKn Edge
Falling XCKn Edge
R/W
15
R
–
7
0
0
R/W
14
R
–
6
0
0
R/W
13
R
–
5
0
0
R/W
12
R
–
4
0
0
UBRR[7:0]
ATmega164P/324P/644P
R/W
R/W
11
3
0
0
Falling XCKn Edge
Received Data Sampled (Input on RxDn
Pin)
Rising XCKn Edge
R/W
R/W
10
2
0
0
UBRR[11:8]
R/W
R/W
9
1
0
0
R/W
R/W
8
0
0
0
UBRRHn
UBRRLn
193