ATMEGA32A-ANR Atmel, ATMEGA32A-ANR Datasheet - Page 181
![IC MCU AVR 32K FLASH 44TQFP](/photos/6/70/67042/313-44-tqfp_sml.jpg)
ATMEGA32A-ANR
Manufacturer Part Number
ATMEGA32A-ANR
Description
IC MCU AVR 32K FLASH 44TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheet
1.ATMEGA32A-MU.pdf
(353 pages)
Specifications of ATMEGA32A-ANR
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 ~ 85°C
Package / Case
44-TQFP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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Manufacturer
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20.4
8155C–AVR–02/11
Multi-master Bus Systems, Arbitration and Synchronization
Figure 20-6. 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:
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.
Figure 20-7. SCL Synchronization between Multiple Masters
Arbitration is carried out by all masters continuously monitoring the SDA line after outputting
data. If the value read from the SDA line does not match the value the master had output, it has
lost the arbitration. Note that a master can only lose arbitration when it outputs a high SDA value
while another master outputs a low value. The losing master should immediately go to slave
• 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,
that is, 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
SCL from
SCL from
Addr MSB
Master A
Master B
SCL bus
1
Line
2
SLA+R/W
Addr LSB
7
R/W
8
TA
Counting Low Period
low
Masters Start
ACK
TB
9
low
Data MSB
1
TA
2
Counting High Period
Data Byte
high
Masters Start
TB
high
7
Data LSB
ATmega32A
8
ACK
9
STOP
181
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