ATMEGA328P-20PU Atmel, ATMEGA328P-20PU Datasheet - Page 213
ATMEGA328P-20PU
Manufacturer Part Number
ATMEGA328P-20PU
Description
Manufacturer
Atmel
Datasheet
1.ATMEGA328P-20PU.pdf
(419 pages)
Specifications of ATMEGA328P-20PU
Cpu Family
ATmega
Device Core
AVR
Device Core Size
8b
Frequency (max)
20MHz
Interface Type
SPI/TWI/USART
Program Memory Type
Flash
Program Memory Size
32KB
Total Internal Ram Size
2KB
# I/os (max)
23
Number Of Timers - General Purpose
3
Operating Supply Voltage (typ)
3.3/5V
Operating Supply Voltage (max)
5.5V
Operating Supply Voltage (min)
2.7V
On-chip Adc
6-chx10-bit
Instruction Set Architecture
RISC
Operating Temp Range
-40C to 85C
Operating Temperature Classification
Industrial
Mounting
Through Hole
Pin Count
28
Package Type
PDIP
Lead Free Status / Rohs Status
Compliant
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21.3
21.3.1
21.3.2
8025K–AVR–10/09
Data Transfer and Frame Format
Transferring Bits
START and STOP Conditions
Each data bit transferred on the TWI bus is accompanied by a pulse on the clock line. The level
of the data line must be stable when the clock line is high. The only exception to this rule is for
generating start and stop conditions.
Figure 21-2. Data Validity
The Master initiates and terminates a data transmission. The transmission is initiated when the
Master issues a START condition on the bus, and it is terminated when the Master issues a
STOP condition. Between a START and a STOP condition, the bus is considered busy, and no
other master should try to seize control of the bus. A special case occurs when a new START
condition is issued between a START and STOP condition. This is referred to as a REPEATED
START condition, and is used when the Master wishes to initiate a new transfer without relin-
quishing control of the bus. After a REPEATED START, the bus is considered busy until the next
STOP. This is identical to the START behavior, and therefore START is used to describe both
START and REPEATED START for the remainder of this datasheet, unless otherwise noted. As
depicted below, START and STOP conditions are signalled by changing the level of the SDA
line when the SCL line is high.
Figure 21-3. START, REPEATED START and STOP conditions
SDA
SCL
START
SDA
SCL
Data Stable
STOP
Data Change
START
ATmega48P/88P/168P
Data Stable
REPEATED START
STOP
213
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