ATMEGA644A-PU Atmel, ATMEGA644A-PU Datasheet - Page 211
ATMEGA644A-PU
Manufacturer Part Number
ATMEGA644A-PU
Description
IC MCU AVR 64K FLASH 40PDIP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA644A-PU
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
40-DIP (0.600", 15.24mm)
Processor Series
ATmega
Core
AVR
Data Bus Width
8 bit
Data Ram Size
4 KB
Interface Type
JTAG, TWI, SPI, USART
Maximum Clock Frequency
20 MHz
Number Of Programmable I/os
32
Number Of Timers
3
Operating Supply Voltage
3.3 V
Maximum Operating Temperature
+ 85 C
Mounting Style
Through Hole
Minimum Operating Temperature
- 40 C
Operating Temperature Range
- 40 C to + 85 C
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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20.3.4
20.3.5
8272A–AVR–01/10
Data Packet Format
Combining Address and Data Packets into a Transmission
All data packets transmitted on the TWI bus are nine bits long, consisting of one data byte and
an acknowledge bit. During a data transfer, the Master generates the clock and the START and
STOP conditions, while the Receiver is responsible for acknowledging the reception. An
Acknowledge (ACK) is signalled by the Receiver pulling the SDA line low during the ninth SCL
cycle. If the Receiver leaves the SDA line high, a NACK is signalled. When the Receiver has
received the last byte, or for some reason cannot receive any more bytes, it should inform the
Transmitter by sending a NACK after the final byte. The MSB of the data byte is transmitted first.
Figure 20-5. Data Packet Format
A transmission basically consists of a START condition, a SLA+R/W, one or more data packets
and a STOP condition. An empty message, consisting of a START followed by a STOP condi-
tion, is illegal. Note that the Wired-ANDing of the SCL line can be used to implement
handshaking between the Master and the Slave. The Slave can extend the SCL low period by
pulling the SCL line low. This is useful if the clock speed set up by the Master is too fast for the
Slave, or the Slave needs extra time for processing between the data transmissions. The Slave
extending the SCL low period will not affect the SCL high period, which is determined by the
Master. As a consequence, the Slave can reduce the TWI data transfer speed by prolonging the
SCL duty cycle.
Figure 20-6 on page 211
transmitted between the SLA+R/W and the STOP condition, depending on the software protocol
implemented by the application software.
Figure 20-6. Typical Data Transmission
164A/164PA/324A/324PA/644A/644PA/1284/1284P
Addr MSB
Aggregate
Transmitter
SDA from
SDA from
SCL from
Receiver
Master
1
SDA
SLA+R/W
2
SLA+R/W
Addr LSB
Data MSB
shows a typical data transmission. Note that several data bytes can be
7
1
R/W
8
2
ACK
9
Data Byte
7
Data MSB
Data LSB
8
1
ACK
2
9
Data Byte
7
STOP, REPEATED
START or Next
Data LSB
Data Byte
8
ACK
9
211
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