ATmega406 Atmel Corporation, ATmega406 Datasheet - Page 142
ATmega406
Manufacturer Part Number
ATmega406
Description
Manufacturer
Atmel Corporation
Specifications of ATmega406
Flash (kbytes)
40 Kbytes
Pin Count
48
Max. Operating Frequency
1 MHz
Cpu
8-bit AVR
# Of Touch Channels
8
Hardware Qtouch Acquisition
No
Max I/o Pins
18
Ext Interrupts
4
Usb Speed
No
Usb Interface
No
Twi (i2c)
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
11
Adc Resolution (bits)
12
Adc Speed (ksps)
1.9
Resistive Touch Screen
No
Temp. Sensor
Yes
Crypto Engine
No
Sram (kbytes)
2
Eeprom (bytes)
512
Self Program Memory
YES
Dram Memory
No
Nand Interface
No
Picopower
No
Temp. Range (deg C)
-30 to 85
I/o Supply Class
4.0 to 25
Operating Voltage (vcc)
4.0 to 25
Fpu
No
Mpu / Mmu
no / no
Timers
2
Output Compare Channels
3
Pwm Channels
2
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
ATmega406-1AAU
Manufacturer:
AT
Quantity:
20 000
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25.4
142
Multi-master Bus Systems, Arbitration and Synchronization
ATmega406
Figure 25-6. 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.
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
8
ACK
9
2548E–AVR–07/06
STOP
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