ST10R272L STMicroelectronics, ST10R272L Datasheet - Page 33

• Manufacturer Part Number: ST10R272L
• Description: 16-BIT Romless MCU WITH MAC UNIT
• Manufacturer: STMicroelectronics

Specifications of ST10R272L

• Cpu Frequency: 0 to 50 MHz
• Power: 3.3 Volt +/-0.3V

ST10R272L - SYSTEM RESET
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SYSTEM RESET
The following type of reset are implemented on the ST10R272L:
Asynchronous hardware reset: Asynchronous reset does not require a stabilized clock
signal on XTAL1 as it is not internally resynchronized, it resets the microcontroller into its
default reset state. Asynchronous reset is required on chip power-up and can be used during
catastrophic situations. The rising edge of the RSTIN pin is internally resynchronized before
exiting the reset condition, therefore, only the entry to hardware reset is asynchronous.
Synchronous hardware reset (warm reset): A warm synchronous hardware reset is
triggered when the reset input signal RSTIN is latched low and Vpp pin is high. The I/Os are
immediately (asynchronously) set in high impedance, RSTOUT is driven low. After RSTIN
negation is detected, a short transition period elapses, during which pending internal hold
states are cancelled and any current internal access cycles are completed, external bus
cycles are aborted. Then, the internal reset sequence is active for 1024 TCL (512 CPU clock
cycles). During this reset sequence, if bit BDRSTEN was previously set by software (bit 3 in
SYSCON register), RSTIN pin is driven low and internal reset signal is asserted to reset the
microcontroller in its default state. Note that after all reset sequence, bit BDRSTEN is cleared.
After the reset sequence has been completed, the RSTIN input is sampled. When the reset
input signal is active at that time the internal reset condition is prolonged until RSTIN
becomes inactive.
Software reset: The reset sequence can be triggered at any time by the protected
instruction SRST (software reset). This instruction can be executed deliberately within a
program, e.g. to leave bootstrap loader mode, or on a hardware trap that reveals a system
failure. As for a synchronous hardware reset, if bit BDRSTEN was previously set by software
(bit 3 in SYSCON register), the reset sequence lasts 1024 TCL (512 CPU clock cycles), and
drives the RSTIN pin low.
Watchdog timer reset: When the watchdog timer is not disabled during the initialization or
serviced regularly during program execution it will overflow and trigger the reset sequence.
Unlike hardware and software resets, the watchdog reset completes a running external bus
cycle if this bus cycle does not use READY, or if READY is sampled active (low) after the
programmed waitstates. When READY is sampled inactive (high) after the programmed
waitstates the running external bus cycle is aborted. Then the internal reset sequence is
started. The watchdog reset cannot occur while the ST10R272L is in bootstrap loader mode.
Bidirectional reset: The bidirectional reset is activated by setting bit BDRSTEN (bit 3 in
SYSCON register). This reset makes the watchdog timer reset and software reset externally
visible. It is active for the duration of an internal reset sequences caused by a watchdog timer
reset and software reset. Therefore, the bidirectional reset transforms an internal watchdog
timer reset or software reset into an external hardware reset with a minimum duration of
1024 TCL.
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