ATMEGA644P-20PQ Atmel, ATMEGA644P-20PQ Datasheet - Page 58

• Manufacturer Part Number: ATMEGA644P-20PQ
• Description: MCU AVR 64K FLASH 20MHZ 40-PDIP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA644P-20PQ

• 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: 64KB (32K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 2K x 8
• Ram Size: 4K 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: 40-DIP (0.600", 15.24mm)
• For Use With: ATSTK600 - DEV KIT FOR AVR/AVR32
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.9
8.9.1
8011O–AVR–07/10
Register Description
MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU reset.
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by
the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or by writing a logic
zero to the flag.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 2 – BORF: Brown-out Reset Flag
This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset Flags to identify a reset condition, the user should read and then
Reset the MCUSR as early as possible in the program. If the register is cleared before another
reset occurs, the source of the reset can be found by examining the Reset Flags.
Bit
0x34 (0x54)
Read/Write
Initial Value
R
7
–
0
R
6
–
0
R
5
–
0
JTRF
R/W
4
ATmega164P/324P/644P
WDRF
R/W
3
See Bit Description
BORF
R/W
2
EXTRF
R/W
1
PORF
R/W
0
MCUSR
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