參數(shù)資料
型號: ST72121J2
元件分類: 8位微控制器
英文描述: 8-bit Microcontroller with 2/4/8K Bytes In-System Programmable Flash
中文描述: 8位微控制器與2/4/8K字節(jié)在系統(tǒng)可編程閃存
文件頁數(shù): 16/93頁
文件大?。?/td> 915K
代理商: ST72121J2
16/93
ST72E121 ST72T121
3.2 RESET
3.2.1 Introduction
There are four sources of Reset:
– RESET pin (external source)
– Power-On Reset (Internal source)
– WATCHDOG (Internal Source)
– Low Voltage Detection Reset (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 for a duration of t
RESET
to reset
the whole application.
3.2.3 Reset Operation
The duration of the Reset state is a minimum of
4096 internal CPU Clock cycles. During the Reset
state, all I/Os take their reset value.
A Reset signal originating from an external source
must have a duration of at least t
PULSE
in order to
be recognised. This detection is asynchronous
and therefore the MCU can enter Reset state even
in Halt mode.
At the end of the Reset cycle, the MCU may be
held in the Reset state by an External Reset sig-
nal. The RESET pin may thus be used to ensure
V
DD
has risen to a point where the MCU can oper-
ate correctly before the user program is run. Fol-
lowing a Reset event, or after exiting Halt mode, a
4096 CPU Clock cycle delay period is initiated in
order to allow the oscillator to stabilise and to en-
sure that recovery has taken place from the Reset
state.
In the high state, the RESET pin is connected in-
ternally to a pull-up resistor (R
ON
). This resistor
can be pulled low by external circuitry to reset the
device.
The RESET pin is an asynchronous signal which
plays a major role in EMS performance. In a noisy
environment, it is recommended to use the exter-
nal connections shown in
Figure 4
.
Figure 11. Reset Block Diagram
INTERNAL
RESET
WATCHDOG RESET
LOW VOLTAGE DETECTOR RESET
OSCILLATOR
SIGNAL
C
RESET
TO ST7
RESET
POWER-ON RESET
V
DD
R
ON
16
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