ST72T311 ST Microelectronics, ST72T311 Datasheet - Page 18

• Manufacturer Part Number: ST72T311
• Description: 8-BIT MCU WITH 8 TO 16K OTP/EPROM
• Manufacturer: ST Microelectronics

ST72E311 ST72T311
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
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
Figure 13. Reset Block Diagram
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RESET
V
DD
OSCILLATOR
SIGNAL
R
ON
PULSE
RESET
in order to
to reset
TO ST7
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
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
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 6.
RESET
DD
has risen to a point where the MCU can oper-
POWER-ON RESET
WATCHDOG RESET
LOW VOLTAGE DETECTOR RESET
ON
INTERNAL
RESET
). This resistor