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参数资料
| 型号： | ST72671N4B1/XXX |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDIP56 |
| 封装： | 0.600 INCH, SHRINK, PLASTIC, DIP-56 |
| 文件页数： | 9/101页 |
| 文件大小： | 608K |
| 代理商： | ST72671N4B1/XXX |
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ST72671
3.2 RESET
3.2.1 Introduction
There are three sources of Reset:
– RESET pin (external source)
– Power-On Reset (Internal source)
– WATCHDOG (Internal Source)
The Reset Service Routine vector is located at ad-
dress FFFEh-FFFFh.
3.2.2 External Reset
The RESET pin is both an input and an open-drain
output with integrated pull-up resistor. When one
of the internal Reset sources is active, the Reset
pin is driven low to reset the whole application.
3.2.3 Reset Operation
The duration of the Reset condition, which is also
reflected on the output pin, is fixed at 4096 internal
CPU Clock cycles. A Reset signal originating from
an external source must have a duration of at least
1.5 internal CPU Clock cycles in order to be recog-
nised. At the end of the Power-On Reset cycle, the
MCU may be held in the Reset condition by an Ex-
ternal Reset signal. The RESET pin may thus be
used to ensure VDD has risen to a point where the
MCU can operate correctly before the user pro-
gram is run. Following a Power-On Reset event, or
after exiting Halt mode, a 4096 CPU Clock cycle
delay period is initiated in order to allow the oscil-
lator to stabilise and to ensure that recovery has
taken place from the Reset state.
During the Reset cycle, the device Reset pin acts
as an output that is pulsed low. In its high state, an
internal pull-up resistor of about 300K
is con-
nected to the Reset pin. This resistor can be pulled
low by external circuitry to reset the device.
3.2.4 Power-on Reset
This circuit detects the ramping up of VDD,and
generates a pulse that is used to reset the applica-
tion (at approximately VDD= 2V).
Power-On Reset is designed exclusively to cope
with power-up conditions, and should not be used
in order to attempt to detect a drop in the power
supply voltage.
Caution:
to re-initialize the Power-On Reset, the
power supply must fall below approximately 0.8V
(Vtn), prior to rising above 2V. If this condition is
not respected, on subsequent power-up the Reset
pulse may not be generated. An external Reset
pulse may be required to correctly reactivate the
circuit.
Figure 9. Reset Block Diagram
INTERNAL
RESET
WATCHDOG RESET
OSCILLATOR
SIGNAL
CO
U
N
T
E
R
RESET
300K
TO ST7
RESET
VDD
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