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Reset Controller Module
Freescale Semiconductor
13-5
Asynchronous reset sources usually indicate a catastrophic failure. Therefore, the reset control logic does
not wait for the current bus cycle to complete. Reset is immediately asserted to the system.
13.4.1.1
Power-On Reset
At power up, the reset controller asserts RSTOUT. RSTOUT continues to be asserted until V
DD
has
reached a minimum acceptable level and, if PLL clock mode is selected, until the PLL achieves phase lock.
After approximately another 512 cycles (non-serial boot) or at the end of the serial boot sequence,
RSTOUT is negated and the device begins operation.
13.4.1.2
External Reset
Asserting the external RESET for at least four rising FB_CLK edges causes the external reset request to
be recognized and latched. After the RESET pin is negated and the PLL has acquired lock, the reset
controller asserts RSTOUT either for approximately 512 bus clock cycles (non-serial boot) or for the
duration of the serial boot sequence. The device then exits reset and begins operation.
In low-power stop mode, the system clocks stop. Asserting the external RESET in stop mode causes an
external reset to be recognized asynchronously.
13.4.1.3
Core Watchdog Timer Reset
A core watchdog timer timeout causes the timer reset request to be recognized and latched. If the RESET
pin is negated and the PLL has acquired lock, the reset controller asserts RSTOUT either for approximately
512 bus clock cycles (non-serial boot) or for the duration of the serial boot sequence. Then the device exits
reset and begins operation.
13.4.1.4
Loss-of-Lock Reset
This reset condition occurs when the PLL loses lock. After the PLL has acquired lock, the reset controller
asserts RSTOUT either for approximately 512 bus clock cycles (non-serial boot) or for the duration of the
serial boot sequence. The device then exits reset and resumes operation.
13.4.1.5
Software Reset
A software reset occurs when the RCR[SOFTRST] bit is set. If the RESET is negated and the PLL has
acquired lock, the reset controller asserts RSTOUT either for approximately 512 bus clock cycles
(non-serial boot) or for the duration of the serial boot sequence. Then the device exits reset and resumes
operation.
13.4.2
Reset Control Flow
The reset logic control flow is shown in
. In this figure, the control state boxes have been
numbered, and these numbers are referred to (within parentheses) in the flow description that follows. All
cycle counts given are approximate.
Содержание MCF54455
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