ATMEGA164P-20MCU Atmel, ATMEGA164P-20MCU Datasheet - Page 214

• Manufacturer Part Number: ATMEGA164P-20MCU
• Description: MCU AVR 16K FLASH 20MHZ 44-QFN
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA164P-20MCU

• 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: 32
• Program Memory Size: 16KB (8K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 1K 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: 44-VQFN Exposed Pad
• For Use With: ATSTK600-TQFP44 - STK600 SOCKET/ADAPTER 44-TQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

18.5.3
18.5.4
18.5.5
8011O–AVR–07/10
Bus Interface Unit
Address Match Unit
Control Unit
• TWBR = Value of the TWI Bit Rate Register.
• TWPS = Value of the prescaler bits in the TWI Status Register.
Note:
This unit contains the Data and Address Shift Register (TWDR), a START/STOP Controller and
Arbitration detection hardware. The TWDR contains the address or data bytes to be transmitted,
or the address or data bytes received. In addition to the 8-bit TWDR, the Bus Interface Unit also
contains a register containing the (N)ACK bit to be transmitted or received. This (N)ACK Regis-
ter is not directly accessible by the application software. However, when receiving, it can be set
or cleared by manipulating the TWI Control Register (TWCR). When in Transmitter mode, the
value of the received (N)ACK bit can be determined by the value in the TWSR.
The START/STOP Controller is responsible for generation and detection of START, REPEATED
START, and STOP conditions. The START/STOP controller is able to detect START and STOP
conditions even when the AVR MCU is in one of the sleep modes, enabling the MCU to wake up
if addressed by a Master.
If the TWI has initiated a transmission as Master, the Arbitration Detection hardware continu-
ously monitors the transmission trying to determine if arbitration is in process. If the TWI has lost
an arbitration, the Control Unit is informed. Correct action can then be taken and appropriate
status codes generated.
The Address Match unit checks if received address bytes match the seven-bit address in the
TWI Address Register (TWAR). If the TWI General Call Recognition Enable (TWGCE) bit in the
TWAR is written to one, all incoming address bits will also be compared against the General Call
address. Upon an address match, the Control Unit is informed, allowing correct action to be
taken. The TWI may or may not acknowledge its address, depending on settings in the TWCR.
The Address Match unit is able to compare addresses even when the AVR MCU is in sleep
mode, enabling the MCU to wake up if addressed by a Master.
If another interrupt (for example, INT0) occurs during TWI Power-down address match and
wakes up the CPU, the TWI aborts operation and return to it’s idle state. If this cause any prob-
lems, ensure that TWI Address Match is the only enabled interrupt when entering Power-
down.
Note:
The Control unit monitors the TWI bus and generates responses corresponding to settings in the
TWI Control Register (TWCR). When an event requiring the attention of the application occurs
on the TWI bus, the TWI Interrupt Flag (TWINT) is asserted. In the next clock cycle, the TWI Sta-
tus Register (TWSR) is updated with a status code identifying the event. The TWSR only
contains relevant status information when the TWI Interrupt Flag is asserted. At all other times,
(1)
Pull-up resistor values should be selected according to the SCL frequency and the capacitive bus
line load. See 2-wire Serial Bus Requirements in
resistor.
1. This only applies to ATmega164P revision A to C, ATmega324P revision A to D, and all
ATmega644P revisions.
SCL frequency
=
---------------------------------------------------------- -
16
CPU Clock frequency
+
ATmega164P/324P/644P
2(TWBR) 4
Table 25-10 on page 333
⋅
TWPS
for value of pull-up
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