參數(shù)資料
型號: PIC16C620A
廠商: Microchip Technology Inc.
元件分類: 8位微控制器
英文描述: EPROM-Based 8-Bit CMOS Microcontroller
中文描述: 存儲器為基礎(chǔ)的8位CMOS微控制器
文件頁數(shù): 50/108頁
文件大?。?/td> 645K
代理商: PIC16C620A
PIC16C62X
DS30235G-page 50
Preliminary
1998 Microchip Technology Inc.
9.4
Power-on Reset (POR), Power-up
Timer (PWRT), Oscillator Start-up
Timer (OST) and Brown-out Reset
(BOR)
9.4.1
POWER-ON RESET (POR)
The on-chip POR circuit holds the chip in reset until
V
DD
has reached a high enough level for proper opera-
tion. To take advantage of the POR, just tie the MCLR
pin through a resistor to V
DD
. This will eliminate exter-
nal RC components usually needed to create Power-on
Reset. A maximum rise time for V
DD
is required. See
Electrical Specifications for details.
The POR circuit does not produce an internal reset
when V
DD
declines.
When the device starts normal operation (exits the
reset condition), device operating parameters (voltage,
frequency, temperature, etc.) must be met to ensure
operation. If these conditions are not met, the device
must be held in reset until the operating conditions are
met.
For additional information, refer to Application Note
AN607 “Power-up Trouble Shooting”.
9.4.2
POWER-UP TIMER (PWRT)
The Power-up Timer provides a fixed 72 ms (nominal)
time-out on power-up only, from POR or Brown-out
Reset. The Power-up Timer operates on an internal RC
oscillator. The chip is kept in reset as long as PWRT is
active. The PWRT delay allows the V
DD
to rise to an
acceptable level. A configuration bit, PWRTE can
disable (if set) or enable (if cleared or programmed) the
Power-up Timer. The Power-up Timer should always be
enabled when Brown-out Reset is enabled.
The Power-Up Time delay will vary from chip to chip
and due to V
DD
, temperature and process variation.
See DC parameters for details.
9.4.3
OSCILLATOR START-UP TIMER (OST)
The Oscillator Start-Up Timer (OST) provides a 1024
oscillator cycle (from OSC1 input) delay after the
PWRT delay is over. This ensures that the crystal
oscillator or resonator has started and stabilized.
The OST time-out is invoked only for XT, LP and HS
modes and only on power-on reset or wake-up from
SLEEP.
9.4.4
BROWN-OUT RESET (BOR)
The PIC16C62X members have on-chip Brown-out
Reset circuitry. A configuration bit, BOREN, can dis-
able (if clear/programmed) or enable (if set) the
Brown-out Reset circuitry. If V
DD
falls below 4.0V refer
to V
BOR
parameter D005(V
BOR
) for greater than
parameter (TBOR) in Table 12-6, the brown-out situa-
tion will reset the chip. A reset is not guaranteed to
occur if V
DD
falls below 4.0V for less than parameter
(TBOR).
On any reset (Power-on, Brown-out, Watchdog, etc.)
the chip will remain in Reset until V
DD
rises above
BV
DD
. The Power-up Timer will now be invoked and will
keep the chip in reset an additional 72 ms.
If V
DD
drops below BV
DD
while the Power-up Timer is
running, the chip will go back into a Brown-out Reset
and the Power-up Timer will be re-initialized. Once V
DD
rises above BV
DD
, the Power-Up Timer will execute a
72 ms reset. The Power-up Timer should always be
enabled when Brown-out Reset is enabled. Figure 9-8
shows typical Brown-out situations.
FIGURE 9-8:
BROWN-OUT SITUATIONS
72 ms
BV
DD
Max.
BV
DD
Min.
V
DD
Internal
Reset
BV
DD
Max.
BV
DD
Min.
V
DD
Internal
Reset
72 ms
<72 ms
72 ms
BV
DD
Max.
BV
DD
Min.
V
DD
Internal
Reset
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