Startup After Power And External Reset - Fujitsu MB96300 series Hardware Manual

MB96300 Super Series Hardware Manual
8.3

Startup after Power and External reset

After a Power or External reset event, the MCU waits for the stabilization of the power
supply and the RC oscillator. Then the MCU starts executing the Boot ROM program with
the RC clock as clock source (RC Run mode).
A transition to another clock mode (Main clock, PLL clock or Sub clock) is possible after
stabilization of the respective clock. The stabilization times for the external oscillators
can be adjusted to the characteristics of the connected oscillators.
■ Reset extension
Power and External reset events are extended by the reset extension circuit to guarantee the stabilization of
the voltage regulators and comparators before program execution starts.
●
Power reset extension
The Power reset extension counter is a 10 bit counter that is initialized by the power-on detector and by a low
voltage reset and that is clocked by the RC clock CLKRC.
This counter keeps the internal Power reset signal PRST active for 700 RC clock cycles after the last power-
on or low voltage event was cleared. PRST is deactivated if the power supply was stable for at least 700 RC
clock cycles (approximately 350µs at 2MHz nominal RC clock frequency).
●
External reset extension
The External reset extension counter is also a 10 bit counter that is initialized by a falling edge at the RST
input pin and that is clocked by the RC clock CLKRC. A Power reset also initializes this counter to achieve a
defined startup time even if the device is started by a Power reset only.
This counter keeps the signal ERST active for 700 RC clock cycles after the last falling edge of the RST
input pin (approximately 350µs at 2MHz nominal RC clock frequency).
If RST is asserted for more than 700 RC clock cycles, then this function has no effect.
Figure 8.3-1 shows a block diagram of the reset extension circuit and Figure 8.3-2 shows a timing diagram of
the External reset extension function.
CHAPTER 8 RESETS AND STARTUP
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