MC68HC05RC17 Datasheet, PDF (50/128 Pages) Freescale Semiconductor, Inc – General Release Specification

Resets
Freescale Semiconductor, Inc.
5.4 Low-Power External Reset (LPRST)
The LPRST pin is one of the two external sources of a reset. This
external reset occurs whenever the LPRST pin is pulled below the lower
threshold and remains in reset until the LPRST pin rises. This active-low
input will, in addition to generating the RST signal and resetting the CPU
and peripherals, halt all internal processor clocks. The MCU will remain
in this low-power reset condition as long as a logic 0 remains on LPRST.
When a logic 1 is applied to LPRST, processor clocks will be re-enabled
with the MCU remaining in reset until the 4064 internal processor clock
cycle (t_cyc) oscillator stabilization delay is completed. If any other reset
function is active at the end of this 4064-cycle delay, the RST signal
remains in the reset condition until the other reset condition(s) end.
5.5 Internal Resets
The three internally generated resets are the initial power-on reset
function, the COP watchdog timer reset, and the illegal address detector.
Termination of the external reset input, external LPRST input, or the
internal COP watchdog timer are the only reset sources that can alter the
operating mode of the MCU. The other internal resets do not have any
effect on the mode of operation when their reset state ends.
5.5.1 Power-On Reset (POR)
The internal POR is generated on power-up to allow the clock oscillator
to stabilize. The POR is strictly for power turn-on conditions and is not
able to detect a drop in the power supply voltage (brown-out). There is
an oscillator stabilization delay of 4064 internal processor bus clock
cycles (PH2) after the oscillator becomes active.
The POR generates the RST signal that resets the CPU. If any other
reset function is active at the end of this 4064-cycle delay, the RST
signal remains in the reset condition until the other reset condition(s)
ends.
General Release Specification
MC68HC05RC17 — Rev. 2.0
Resets
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