ATMEGA128L-8AJ Atmel, ATMEGA128L-8AJ Datasheet - Page 225
![IC MCU AVR 128K 8MHZ LV 64-TQFP](/photos/12/13/121332/313-64-tqfp_sml.jpg)
ATMEGA128L-8AJ
Manufacturer Part Number
ATMEGA128L-8AJ
Description
IC MCU AVR 128K 8MHZ LV 64-TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA128L-8AJ
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
53
Program Memory Size
128KB (64K x 16)
Program Memory Type
FLASH
Eeprom Size
4K 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
64-TQFP, 64-VQFP
For Use With
ATSTK501 - ADAPTER KIT FOR 64PIN AVR MCU
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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Multi-master
Systems and
Arbitration
2467V–AVR–02/11
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 105. An Arbitration Example
Several different scenarios may arise during arbitration, as described below:
•
•
•
This is summarized in
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.
Two or more masters are accessing different slaves. In this case, arbitration will occur in the
SLA bits. Masters trying to output a one on SDA while another master outputs a zero will
lose the arbitration. Masters losing arbitration in SLA will switch to slave mode to check if
they are being addressed by the winning master. If addressed, they will switch to SR or ST
mode, depending on the value of the READ/WRITE bit. If they are not being addressed, they
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.
SDA
SCL
TRANSMITTER
Device 1
MASTER
Figure
106. Possible status values are given in circles.
TRANSMITTER
Device 2
MASTER
Device 3
RECEIVER
SLAVE
........
Device n
V
CC
ATmega128
R1
R2
225
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