参数资料
型号: ST72324BLK4BA/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, PDIP32
封装: 0.400 INCH, PLASTIC, SDIP-32
文件页数: 69/151页
文件大小: 1209K
代理商: ST72324BLK4BA/XXX
ST72F324L, ST72324BL
24/151
6.3 RESET SEQUENCE MANAGER (RSM)
6.3.1 Introduction
The reset sequence manager includes two RE-
SET sources as shown in Figure 12:
External RESET source pulse
Internal WATCHDOG RESET
These sources act on the RESET pin and it is al-
ways kept low during the delay phase.
The RESET service routine vector is fixed at ad-
dresses FFFEh-FFFFh in the ST7 memory map.
The basic RESET sequence consists of 3 phases
as shown in Figure 11:
Active Phase depending on the RESET source
256 or 4096 CPU clock cycle delay (selected by
option byte)
RESET vector fetch
The 256 or 4096 CPU clock cycle delay allows the
oscillator to stabilise and ensures that recovery
has taken place from the Reset state. The shorter
or longer clock cycle delay should be selected by
option byte to correspond to the stabilization time
of the external oscillator used in the application.
The RESET vector fetch phase duration is 2 clock
cycles.
Figure 11. RESET Sequence Phases
6.3.2 Asynchronous External RESET pin
The RESET pin is both an input and an open-drain
output with integrated RON weak pull-up resistor.
This pull-up has no fixed value but varies in ac-
cordance with the input voltage. It can be pulled
low by external circuitry to reset the device. See
Electrical Characteristic section for more details.
A RESET signal originating from an external
source must have a duration of at least th(RSTL)in in
order to be recognized. This detection is asynchro-
nous and therefore the MCU can enter reset state
even in HALT mode.
The RESET pin is an asynchronous signal which
plays a major role in EMS performance. In a noisy
environment, it is recommended to follow the
guidelines mentioned in the electrical characteris-
tics section.
6.3.3 External Power-On RESET
To start up the microcontroller correctly, the user
must ensure by means of an external reset circuit
that the reset signal is held low until VDD is over
the minimum level specified for the selected fOSC
frequency.
A proper reset signal for a slow rising VDD supply
can generally be provided by an external RC net-
work connected to the RESET pin.
6.3.4 Internal Watchdog RESET
Starting from the Watchdog counter underflow, the
device RESET pin acts as an output that is pulled
low during at least tw(RSTL)out.
Figure 12. Reset Block Diagram
RESET
Active Phase
INTERNAL RESET
256 or 4096 CLOCK CYCLES
FETCH
VECTOR
RESET
RON
VDD
WATCHDOG RESET
INTERNAL
RESET
PULSE
GENERATOR
Filter
1
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