ATMEGA8A-MUR Atmel, ATMEGA8A-MUR Datasheet - Page 170
ATMEGA8A-MUR
Manufacturer Part Number
ATMEGA8A-MUR
Description
MCU AVR 8KB FLASH 16MHZ 32QFN
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheet
1.ATMEGA8A-MU.pdf
(308 pages)
Specifications of ATMEGA8A-MUR
Core Processor
AVR
Core Size
8-Bit
Speed
16MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
23
Program Memory Size
8KB (4K x 16)
Program Memory Type
FLASH
Eeprom Size
512 x 8
Ram Size
1K 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
*
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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20.4.4
20.4.5
8159D–AVR–02/11
Data Packet Format
Combining Address and Data Packets into a Transmission
Figure 20-5. Address Packet Format
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 20-6. 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 20-7
between the SLA+R/W and the STOP condition, depending on the software protocol imple-
mented by the application software.
Transmitter
Aggregate
SDA from
SDA from
SCL from
Receiver
SDA
SCL
Master
SDA
SLA+R/W
shows a typical data transmission. Note that several data bytes can be transmitted
START
Data MSB
Addr MSB
1
1
2
2
Data Byte
7
Data LSB
Addr LSB
8
7
ACK
9
R/W
8
ATmega8A
ACK
STOP, REPEATED
9
START or Next
Data Byte
170
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