ATMEGA48P-20MMUR Atmel, ATMEGA48P-20MMUR Datasheet - Page 216
![MCU AVR 4K FLASH 20MHZ 28QFN](/photos/12/32/123209/28m1-vqfn_sml.jpg)
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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21.3.5
Figure 21-6. Typical Data Transmission
21.4
8025L–AVR–7/10
SDA
SCL
START
Multi-master Bus Systems, Arbitration and Synchronization
Combining Address and Data Packets into a Transmission
Addr MSB
1
2
Figure 21-5. Data Packet Format
A transmission basically consists of a START condition, a SLA+R/W, one or more data packets
and a STOP condition. An empty message, consisting of a START followed by a STOP condi-
tion, is illegal. Note that the Wired-ANDing of the SCL line can be used to implement
handshaking between the Master and the Slave. The Slave can extend the SCL low period by
pulling the SCL line low. This is useful if the clock speed set up by the Master is too fast for the
Slave, or the Slave needs extra time for processing between the data transmissions. The Slave
extending the SCL low period will not affect the SCL high period, which is determined by the
Master. As a consequence, the Slave can reduce the TWI data transfer speed by prolonging the
SCL duty cycle.
Figure 21-6
between the SLA+R/W and the STOP condition, depending on the software protocol imple-
mented by the application software.
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
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
Transmitter
Aggregate
SLA+R/W
SDA from
SDA from
SCL from
Receiver
Master
SDA
Addr LSB
SLA+R/W
7
shows a typical data transmission. Note that several data bytes can be transmitted
R/W
8
ACK
Data MSB
9
1
2
Data MSB
1
Data Byte
7
2
Data Byte
ATmega48P/88P/168P
Data LSB
8
7
ACK
9
Data LSB
8
ACK
STOP, REPEATED
9
START or Next
Data Byte
STOP
216
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