Добавил:

Upload Опубликованный материал нарушает ваши авторские права? Сообщите нам.

Вуз:

Рыбницкий Филиал Приднестровского Государственного Университета им.Т.Г.Шевченко

Предмет:

[НЕСОРТИРОВАННОЕ]

Файл:

AVR / datasheets / atmega_128.pdf

Скачиваний:

Добавлен:

20.03.2015

Размер:

3.56 Mб

Скачать

☆

<<< < Предыдущая 4 5 6 7 8 9 10 11 12 13 14 1516 / 8316 17 18 19 20 21 22 23 24 25 26 27 28 > Следующая >>>

ATmega128

2. VBOT may be below nominal minimum operating voltage for some devices. For

devices where this is the case, the device is tested down to VCC = VBOT during the

production test. This guarantees that a Brown-out Reset will occur before VCC drops

to a voltage where correct operation of the microcontroller is no longer guaranteed.

The test is performed using BODLEVEL=1 for ATmega128L and BODLEVEL=0 for

ATmega128. BODLEVEL=1 is not applicable for ATmega128.

Power-on Reset

A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detec-

tion level is defined in Table 19. The POR is activated whenever VCC is below the

detection level. The POR circuit can be used to trigger the Start-up Reset, as well as to

detect a failure in supply voltage.

A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reach-

ing the Power-on Reset threshold voltage invokes the delay counter, which determines

how long the device is kept in RESET after VCC rise. The RESET signal is activated

again, without any delay, when VCC decreases below the detection level.

Figure 23. MCU Start-up,

Tied to VCC.

RESET

VCC

VPOT

VRST

RESET

TIME-OUT

tTOUT

INTERNAL

RESET

Figure 24. MCU Start-up,

Extended Externally

RESET

VCC

VPOT

VRST

RESET

TIME-OUT

tTOUT

INTERNAL

External Reset

RESET

An External Reset is generated by a low level on the

pin. Reset pulses longer

RESET

than the minimum pulse width (see Table 19) will generate a reset, even if the clock is

not running. Shorter pulses are not guaranteed to generate a reset. When the applied

signal reaches the Reset Threshold Voltage – VRST on its positive edge, the delay counter starts the MCU after the Time-out period tTOUT has expired.

2467K–AVR–04/04

Figure 25. External Reset During Operation

Brown-out Detection	ATmega128 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC
	level during operation by comparing it to a fixed trigger level. The trigger level for the
	BOD can be selected by the fuse BODLEVEL to be 2.7V (BODLEVEL unprogrammed),
	or 4.0V (BODLEVEL programmed). The trigger level has a hysteresis to ensure spike
	free Brown-out Detection. The hysteresis on the detection level should be interpreted as
	VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
	The BOD circuit can be enabled/disabled by the fuse BODEN. When the BOD is
	enabled (BODEN programmed), and VCC decreases to a value below the trigger level
	(VBOT- in Figure 26), the Brown-out Reset is immediately activated. When VCC increases
	above the trigger level (VBOT+ in Figure 26), the delay counter starts the MCU after the
	time-out period tTOUT has expired.
	The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level
	for longer than tBOD given in Table 19.
	Figure 26. Brown-out Reset During Operation

VCC	VBOT+
	VBOT-
RESET
TIME-OUT	tTOUT
INTERNAL
RESET

50 ATmega128

2467K–AVR–04/04

ATmega128

Watchdog Reset

When the Watchdog times out, it will generate a short reset pulse of 1 CK cycle dura-

tion. On the falling edge of this pulse, the delay timer starts counting the Time-out period

tTOUT. Refer to page 52 for details on operation of the Watchdog Timer.

Figure 27. Watchdog Reset During Operation

MCU Control and Status	The MCU Control and Status Register provides information on which reset source
Register – MCUCSR	caused an MCU reset.
	Bit	7	6	5	4	3	2	1	0

		JTD	–	–	JTRF	WDRF	BORF	EXTRF	PORF	MCUCSR
	Read/Write	R/W	R	R	R/W	R/W	R/W	R/W	R/W
	Initial Value	0	0	0		See Bit Description

Note that only EXTRF and PORF are available in ATmega103 compatibility mode.

• 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 MCUCSR 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.

2467K–AVR–04/04

<<< < Предыдущая 4 5 6 7 8 9 10 11 12 13 14 1516 / 8316 17 18 19 20 21 22 23 24 25 26 27 28 > Следующая >>>

Соседние файлы в папке datasheets

#
20.03.20152.88 Mб44AT90USB82_162.pdf
#
20.03.20154.51 Mб71atmega128.pdf
#
20.03.20155.63 Mб90atmega16.pdf
#
20.03.201538.97 Кб32atmega8melkaya.bak
#
20.03.201539.88 Кб34atmega8melkaya.lay
#
20.03.20153.56 Mб49atmega_128.pdf
#
20.03.20154.86 Mб77atmega_48_88_168.pdf
#
20.03.20155.67 Mб71atmega_8.pdf
#
20.03.20152.47 Mб53atmega_8535.pdf
#
20.03.20151.15 Mб55attiny_11_12.pdf
#
20.03.20151.19 Mб63attiny_13.pdf

Power-on Reset

External Reset

Brown-out Detection

Watchdog Reset