ATMEGA644PA-AUR Atmel, ATMEGA644PA-AUR Datasheet - Page 210
ATMEGA644PA-AUR
Manufacturer Part Number
ATMEGA644PA-AUR
Description
IC MCU AVR 64K FLASH 44TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA644PA-AUR
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)
1.8 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
44-TQFP, 44-VQFP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
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Manufacturer
Quantity
Price
Company:
Part Number:
ATMEGA644PA-AUR
Manufacturer:
ATMEL
Quantity:
1 400
Part Number:
ATMEGA644PA-AUR
Manufacturer:
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20.3.3
8272A–AVR–01/10
Address Packet Format
depicted below, START and STOP conditions are signalled by changing the level of the SDA
line when the SCL line is high.
Figure 20-3. START, REPEATED START and STOP conditions
All address packets transmitted on the TWI bus are 9 bits long, consisting of 7 address bits, one
READ/WRITE control bit and an acknowledge bit. If the READ/WRITE bit is set, a read opera-
tion is to be performed, otherwise a write operation should be performed. When a Slave
recognizes that it is being addressed, it should acknowledge by pulling SDA low in the ninth SCL
(ACK) cycle. If the addressed Slave is busy, or for some other reason can not service the Mas-
ter’s request, the SDA line should be left high in the ACK clock cycle. The Master can then
transmit a STOP condition, or a REPEATED START condition to initiate a new transmission. An
address packet consisting of a slave address and a READ or a WRITE bit is called SLA+R or
SLA+W, respectively.
The MSB of the address byte is transmitted first. Slave addresses can freely be allocated by the
designer, but the address 0000 000 is reserved for a general call.
When a general call is issued, all slaves should respond by pulling the SDA line low in the ACK
cycle. A general call is used when a Master wishes to transmit the same message to several
slaves in the system. When the general call address followed by a Write bit is transmitted on the
bus, all slaves set up to acknowledge the general call will pull the SDA line low in the ack cycle.
The following data packets will then be received by all the slaves that acknowledged the general
call. Note that transmitting the general call address followed by a Read bit is meaningless, as
this would cause contention if several slaves started transmitting different data.
All addresses of the format 1111 xxx should be reserved for future purposes.
Figure 20-4. Address Packet Format
164A/164PA/324A/324PA/644A/644PA/1284/1284P
SDA
SCL
SDA
SCL
START
START
Addr MSB
1
STOP
2
START
Addr LSB
7
REPEATED START
R/W
8
ACK
9
STOP
210
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