ST10F271B datasheet(81/180 Pages) STMICROELECTRONICS

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ST10F271B/ST10F271E

System reset

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20.2

Asynchronous reset

An asynchronous reset is triggered when RSTIN pin is pulled low while RPD pin is at low

level. Then the ST10F271 is immediately (after the input filter delay) forced in reset default

state. It pulls low RSTOUT pin, it cancels pending internal hold states if any, it aborts all

internal/external bus cycles, it switches buses (data, address and control signals) and I/O

pin drivers to high-impedance, it pulls high Port0 pins.

Note:

If an asynchronous reset occurs during a read or write phase in internal memories, the

content of the memory itself could be corrupted: to avoid this, synchronous reset usage is

strongly recommended.

Power-on reset

The asynchronous reset must be used during the power-on of the device. Depending

on crystal or resonator frequency, the on-chip oscillator needs about 1ms to 10ms to

stabilize (Refer to Electrical Characteristics Section), with an already stable VDD. The logic

of the ST10F271 does not need a stabilized clock signal to detect an asynchronous reset,

so it is suitable for power-on conditions. To ensure a proper reset sequence, the RSTIN pin

and the RPD pin must be held at low level until the device clock signal is stabilized and the

system configuration value on Port0 is settled.

At Power-on it is important to respect some additional constraints introduced by the start-up

phase of the different embedded modules.

In particular the on-chip voltage regulator needs at least 1ms to stabilize the internal 1.8V

for the core logic: this time is computed from when the external reference (VDD) becomes

stable (inside specification range, that is at least 4.5V). This is a constraint for the

application hardware (external voltage regulator): the RSTIN pin assertion shall be extended

to guarantee the voltage regulator stabilization.

A second constraint is imposed by the embedded FLASH. When booting from internal

memory, starting from RSTIN releasing, it needs a maximum of 1ms for its initialization:

before that, the internal reset (RST signal) is not released, so the CPU does not start code

execution in internal memory.

Note:

This is not true if external memory is used (pin EA held low during reset phase). In this case,

once RSTIN pin is released, and after few CPU clock (Filter delay plus 3...8 TCL), the

internal reset signal RST is released as well, so the code execution can start immediately

after. Obviously, an eventual access to the data in internal Flash is forbidden before its

initialization phase is completed: an eventual access during starting phase will return FFFFh

(just at the beginning), while later 009Bh (an illegal opcode trap can be generated).

At Power-on, the RSTIN pin shall be tied low for a minimum time that includes also the start-

up time of the main oscillator (tSTUP = 1ms for resonator, 10ms for crystal) and PLL

synchronization time (tPSUP = 200µs): this means that if the internal FLASH is used, the

RSTIN pin could be released before the main oscillator and PLL are stable to recover some

time in the start-up phase (FLASH initialization only needs stable V18, but does not need

stable system clock since an internal dedicated oscillator is used).

Warning:

It is recommended to provide the external hardware with a

current limitation circuitry. This is necessary to avoid

permanent damages of the device during the power-on

transient, when the capacitance on V18 pin is charged. For

the on-chip voltage regulator functionality 10nF are

ST10F271B データシート(PDF) 81 Page - STMicroelectronics

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