ATMEGA324P-A15MZ Atmel, ATMEGA324P-A15MZ Datasheet - Page 171

• Manufacturer Part Number: ATMEGA324P-A15MZ
• Description: MCU AVR 32KB FLASH 15MHZ 44-VQFN
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA324P-A15MZ

• Package / Case: 44-VQFN Exposed Pad
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Speed: 16MHz
• Number Of I /o: 32
• Eeprom Size: 1K x 8
• Core Processor: AVR
• Program Memory Type: FLASH
• Ram Size: 2K x 8
• Program Memory Size: 32KB (32K x 8)
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Connectivity: I²C, SPI, UART/USART
• Core Size: 8-Bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Address Packet
Format
Data Packet Format
2503N–AVR–06/08
Figure 78. START, REPEATED START, and STOP Conditions
All address packets transmitted on the TWI bus are nine bits long, consisting of seven address
bits, one READ/WRITE control bit and an acknowledge bit. If the READ/WRITE bit is set, a read
operation 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 79. 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.
SDA
SCL
SDA
SCL
START
START
Addr MSB
1
STOP START
2
Addr LSB
7
REPEATED START
R/W
8
ATmega32(L)
ACK
9
STOP
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