ATMEGA328P-20PU Atmel, ATMEGA328P-20PU Datasheet - Page 238

• Manufacturer Part Number: ATMEGA328P-20PU
• Manufacturer: Atmel

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

21.9
21.9.1
21.9.2
8025K–AVR–10/09
Register Description
TWBR – TWI Bit Rate Register
TWCR – TWI Control Register
• Two or more masters are accessing different slaves. In this case, arbitration will occur in the
This is summarized in
Figure 21-21. Possible Status Codes Caused by Arbitration
• Bits 7..0 – TWI Bit Rate Register
TWBR selects the division factor for the bit rate generator. The bit rate generator is a frequency
divider which generates the SCL clock frequency in the Master modes. See
Unit” on page 218
The TWCR is used to control the operation of the TWI. It is used to enable the TWI, to initiate a
Master access by applying a START condition to the bus, to generate a Receiver acknowledge,
to generate a stop condition, and to control halting of the bus while the data to be written to the
bus are written to the TWDR. It also indicates a write collision if data is attempted written to
TWDR while the register is inaccessible.
Bit
(0xB8)
Read/Write
Initial Value
Bit
(0xBC)
Read/Write
Initial Value
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.
START
TWBR7
TWINT
R/W
R/W
7
0
7
0
for calculating bit rates.
Address / General Call
Figure
Direction
received
Own
TWBR6
TWEA
R/W
R/W
Yes
Arbitration lost in SLA
6
0
6
0
SLA
21-21. Possible status values are given in circles.
Write
Read
TWBR5
TWSTA
R/W
R/W
No
5
0
5
0
TWSTO
TWBR4
R/W
R/W
4
0
4
0
68/78
38
B0
Arbitration lost in Data
TWBR3
TWWC
TWI bus will be released and not addressed slave mode will be entered
A START condition will be transmitted when the bus becomes free
Data byte will be received and NOT ACK will be returned
Data byte will be received and ACK will be returned
Last data byte will be transmitted and NOT ACK should be received
Data byte will be transmitted and ACK should be received
R/W
R
3
0
3
0
ATmega48P/88P/168P
Data
TWBR2
TWEN
R/W
R/W
2
0
2
0
TWBR1
R/W
R
1
0
1
–
0
”Bit Rate Generator
TWBR0
TWIE
R/W
R/W
0
0
0
0
STOP
TWBR
TWCR
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