ATMEGA328P-20PU Atmel, ATMEGA328P-20PU Datasheet - Page 240
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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21.9.3
21.9.4
8025K–AVR–10/09
TWSR – TWI Status Register
TWDR – TWI Data Register
• Bit 0 – TWIE: TWI Interrupt Enable
When this bit is written to one, and the I-bit in SREG is set, the TWI interrupt request will be acti-
vated for as long as the TWINT Flag is high.
• Bits 7..3 – TWS: TWI Status
These 5 bits reflect the status of the TWI logic and the 2-wire Serial Bus. The different status
codes are described later in this section. Note that the value read from TWSR contains both the
5-bit status value and the 2-bit prescaler value. The application designer should mask the pres-
caler bits to zero when checking the Status bits. This makes status checking independent of
prescaler setting. This approach is used in this datasheet, unless otherwise noted.
• Bit 2 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bits 1..0 – TWPS: TWI Prescaler Bits
These bits can be read and written, and control the bit rate prescaler.
Table 21-7.
To calculate bit rates, see
used in the equation.
In Transmit mode, TWDR contains the next byte to be transmitted. In Receive mode, the TWDR
contains the last byte received. It is writable while the TWI is not in the process of shifting a byte.
This occurs when the TWI Interrupt Flag (TWINT) is set by hardware. Note that the Data Regis-
ter cannot be initialized by the user before the first interrupt occurs. The data in TWDR remains
stable as long as TWINT is set. While data is shifted out, data on the bus is simultaneously
shifted in. TWDR always contains the last byte present on the bus, except after a wake up from
a sleep mode by the TWI interrupt. In this case, the contents of TWDR is undefined. In the case
Bit
(0xB9)
Read/Write
Initial Value
Bit
(0xBB)
Read/Write
Initial Value
TWPS1
0
0
1
1
TWI Bit Rate Prescaler
TWS7
TWD7
R/W
R
7
1
7
1
TWD6
TWS6
R/W
TWPS0
0
1
0
1
R
6
1
6
1
”Bit Rate Generator Unit” on page
TWD5
TWS5
R/W
R
5
1
5
1
TWD4
TWS4
R/W
R
4
1
4
1
Prescaler Value
1
4
16
64
TWD3
TWS3
R/W
R
3
1
3
1
ATmega48P/88P/168P
TWD2
R/W
R
2
1
2
–
0
218. The value of TWPS1..0 is
TWPS1
TWD1
R/W
R/W
1
1
1
0
TWPS0
TWD0
R/W
R/W
0
1
0
0
TWDR
TWSR
240
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