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ST10F296E
System reset
20.2
Asynchronous reset
An asynchronous reset is triggered when the RSTIN pin is pulled low while the RPD pin is at
low level. The ST10F296E device is immediately (after the input filter delay) forced into a
reset default state. It pulls the RSTOUT pin low, 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, and it pulls the Port 0 pins high.
Note:
If an asynchronous reset occurs in the internal memories during a read or write phase, the
content of the memory itself could be corrupted. To avoid this, synchronous reset usage is
strongly recommended.
20.2.1
Power-on reset
The asynchronous reset must be used during the power-on of the device. Depending on the
crystal or resonator frequency, the on-chip oscillator needs about 1 ms to 10 ms to stabilize
ST10F296E 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 low until the device clock signal is stabilized and the system
configuration value on Port 0 has 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 1 ms to stabilize the internal 1.8 V
for the core logic. This time is computed from when the external reference (VDD) becomes
stable inside the specification range (that is at least 4.5 V). This is a constraint for the
application hardware (external voltage regulator). The RSTIN pin assertion must be
extended to guarantee the voltage regulator stabilization.
A second constraint is imposed by the embedded Flash. When booting from the internal
memory, starting from the RSTIN pin being released, the Flash needs a maximum of 1 ms
for its initialization. Before this, the internal reset (RST signal) is not released, so the CPU
does not start code execution in internal memory.
Note:
The above is not true if the external memory is used (pin EA held low during reset phase). In
this case, once the RSTIN pin is released, and after a few CPU clock (filter delay plus 3...8
TCL), the internal reset signal RST is released, afterwhich code execution can start
immediately. Eventual access to the data in the internal Flash is forbidden before its
initialization phase is complete. An eventual access during the starting phase returns FFFFh
at the beginning and 009Bh later on (an illegal opcode trap can be generated).
At power-on, the RSTIN pin must be tied low for a minimum period of time that includes the
start-up time of the main oscillator (tSTUP = 1 ms for the resonator, 10 ms for the crystal) and
the PLL synchronization time (tPSUP = 200 s). Consequently, if the internal Flash is used,
the RSTIN pin could be released to recover some time in the start-up phase (Flash
initialization needs a stable V18, but, does not need a stable system clock since an internal
dedicated oscillator is used) before the main oscillator and PLL are stable.