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ST10F273Z4 Datasheet(PDF) 80 Page - STMicroelectronics |
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ST10F273Z4 Datasheet(HTML) 80 Page - STMicroelectronics |
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80 / 188 page  System reset ST10F273Z4 80/188 20.2 Asynchronous reset An asynchronous reset is triggered when RSTIN pin is pulled low while RPD pin is at low level. Then the ST10F273Z4 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 ST10F273Z4 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 |
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