ATMEGA64A-MN Atmel, ATMEGA64A-MN Datasheet - Page 207
ATMEGA64A-MN
Manufacturer Part Number
ATMEGA64A-MN
Description
IC MCU AVR 64K FLASH 8QFN
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheet
1.ATMEGA64A-AU.pdf
(392 pages)
Specifications of ATMEGA64A-MN
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
53
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)
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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21.5
8160C–AVR–07/09
Multi-master Bus Systems, Arbitration and Synchronization
Figure 21-7. 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:
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.
• 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
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.
SDA
SCL
START
Addr MSB
1
2
SLA+R/W
Addr LSB
7
R/W
8
ACK
9
Data MSB
1
2
Data Byte
7
Data LSB
ATmega64A
8
ACK
9
STOP
207
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