ATMEGA324P-15MZ Atmel, ATMEGA324P-15MZ Datasheet - Page 213
![MCU AVR 32K FLASH 15MHZ 44-QFN](/photos/12/13/121316/313-44-qfn_sml.jpg)
ATMEGA324P-15MZ
Manufacturer Part Number
ATMEGA324P-15MZ
Description
MCU AVR 32K FLASH 15MHZ 44-QFN
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA324P-15MZ
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
32
Program Memory Size
32KB (16K x 16)
Program Memory Type
FLASH
Eeprom Size
1K x 8
Ram Size
2K x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 125°C
Package / Case
44-VQFN
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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19.3.5
19.4
7674F–AVR–09/09
Multi-master Bus Systems, Arbitration and Synchronization
Combining Address and Data Packets into a Transmission
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 19-6 on page 213
transmitted between the SLA+R/W and the STOP condition, depending on the software protocol
implemented by the application software.
Figure 19-6. Typical Data Transmission
The TWI protocol allows bus systems with several masters. Special concerns have been taken
in order to ensure that transmissions will proceed as normal, even if two or more masters initiate
a transmission at the same time. Two problems arise in multi-master systems:
• An algorithm must be implemented allowing only one of the masters to complete the
• Different masters may use different SCL frequencies. A scheme must be devised to
The wired-ANDing of the bus lines is used to solve both these problems. The serial clocks from
all masters will be wired-ANDed, yielding a combined clock with a high period equal to the one
from the Master with the shortest high period. The low period of the combined clock is equal to
the low period of the Master with the longest low period. Note that all masters listen to the SCL
line, effectively starting to count their SCL high and low time-out periods when the combined
SCL line goes high or low, respectively.
transmission. All other masters should cease transmission when they discover that they have
lost the selection process. This selection process is called arbitration. When a contending
master discovers that it has lost the arbitration process, it should immediately switch to Slave
mode to check whether it is being addressed by the winning master. The fact that multiple
masters have started transmission at the same time should not be detectable to the slaves, i.e.
the data being transferred on the bus must not be corrupted.
synchronize the serial clocks from all masters, in order to let the transmission proceed in a
lockstep fashion. This will facilitate the arbitration process.
Addr MSB
1
2
SLA+R/W
Addr LSB
shows a typical data transmission. Note that several data bytes can be
7
R/W
8
ACK
9
ATmega164P/324P/644P
Data MSB
1
2
Data Byte
7
Data LSB
8
ACK
9
213
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