ATMEGA48P-20MMUR Atmel, ATMEGA48P-20MMUR Datasheet - Page 217
ATMEGA48P-20MMUR
Manufacturer Part Number
ATMEGA48P-20MMUR
Description
MCU AVR 4K FLASH 20MHZ 28QFN
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheet
1.ATMEGA168P-20AU.pdf
(420 pages)
Specifications of ATMEGA48P-20MMUR
Core Processor
AVR
Core Size
8-Bit
Speed
20MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
23
Program Memory Size
4KB (2K x 16)
Program Memory Type
FLASH
Eeprom Size
256 x 8
Ram Size
512 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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8025L–AVR–7/10
• 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.
Figure 21-7. 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
mode, checking if it is being addressed by the winning Master. The SDA line should be left high,
but losing masters are allowed to generate a clock signal until the end of the current data or
address packet. Arbitration will continue until only one Master remains, and this may take many
bits. If several masters are trying to address the same Slave, arbitration will continue into the
data packet.
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.
SCL from
SCL from
Master A
Master B
SCL Bus
Line
TA
Counting Low Period
low
Masters Start
TB
low
ATmega48P/88P/168P
TA
Counting High Period
high
Masters Start
TB
high
217
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