ATMEGA2561V-8AU Atmel, ATMEGA2561V-8AU Datasheet - Page 265
ATMEGA2561V-8AU
Manufacturer Part Number
ATMEGA2561V-8AU
Description
IC AVR MCU 256K 8MHZ 64TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA2561V-8AU
Core Processor
AVR
Core Size
8-Bit
Speed
8MHz
Connectivity
EBI/EMI, I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
54
Program Memory Size
256KB (128K x 16)
Program Memory Type
FLASH
Eeprom Size
4K x 8
Ram Size
8K x 8
Voltage - Supply (vcc/vdd)
1.8 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
64-TQFP, 64-VQFP
Processor Series
ATMEGA256x
Core
AVR8
Data Bus Width
8 bit
Data Ram Size
8 KB
Interface Type
2-Wire/SPI/USART
Maximum Clock Frequency
8 MHz
Number Of Programmable I/os
54
Number Of Timers
6
Operating Supply Voltage
1.8 V to 5.5 V
Maximum Operating Temperature
+ 85 C
Mounting Style
SMD/SMT
Minimum Operating Temperature
- 40 C
On-chip Adc
8-ch x 10-bit
For Use With
ATSTK600-TQFP64 - STK600 SOCKET/ADAPTER 64-TQFP770-1007 - ISP 4PORT ATMEL AVR MCU SPI/JTAG770-1005 - ISP 4PORT FOR ATMEL AVR MCU JTAG770-1004 - ISP 4PORT FOR ATMEL AVR MCU SPIATAVRISP2 - PROGRAMMER AVR IN SYSTEM
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
ATMEGA2561V-8AU
Manufacturer:
ATMEL/爱特梅尔
Quantity:
20 000
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23.8
2549M–AVR–09/10
Multi-master Systems and Arbitration
Note that data is transmitted both from Master to Slave and vice versa. The Master must instruct
the Slave what location it wants to read, requiring the use of the MT mode. Subsequently, data
must be read from the Slave, implying the use of the MR mode. Thus, the transfer direction must
be changed. The Master must keep control of the bus during all these steps, and the steps
should be carried out as an atomical operation. If this principle is violated in a multimaster sys-
tem, another Master can alter the data pointer in the EEPROM between steps 2 and 3, and the
Master will read the wrong data location. Such a change in transfer direction is accomplished by
transmitting a REPEATED START between the transmission of the address byte and reception
of the data. After a REPEATED START, the Master keeps ownership of the bus. The following
figure shows the flow in this transfer.
Figure 23-19. Combining Several TWI Modes to Access a Serial EEPROM
If multiple masters are connected to the same bus, transmissions may be initiated simultane-
ously by one or more of them. The TWI standard ensures that such situations are handled in
such a way that one of the masters will be allowed to proceed with the transfer, and that no data
will be lost in the process. An example of an arbitration situation is depicted below, where two
masters are trying to transmit data to a Slave Receiver.
Figure 23-20. An Arbitration Example
Several different scenarios may arise during arbitration, as described below:
•
•
Two or more masters are performing identical communication with the same Slave. In this
case, neither the Slave nor any of the masters will know about the bus contention.
Two or more masters are accessing the same Slave with different data or direction bit. In this
case, arbitration will occur, either in the READ/WRITE bit or in the data bits. The masters
trying to output a one on SDA while another Master outputs a zero will lose the arbitration.
Losing masters will switch to not addressed Slave mode or wait until the bus is free and
transmit a new START condition, depending on application software action.
S
S = START
SDA
SCL
Transmitted from master to slave
SLA+W
TRANSMITTER
Device 1
MASTER
A
Master Transmitter
ADDRESS
TRANSMITTER
ATmega640/1280/1281/2560/2561
Device 2
MASTER
Device 3
RECEIVER
A
SLAVE
Rs = REPEATED START
Rs
Transmitted from slave to master
........
SLA+R
Device n
V
CC
A
Master Receiver
R1
DATA
R2
P = STOP
A
P
265
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