HC705RC16GRSSLASHD datasheet(46/120 Pages) NXP

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Resets

General Release Specification

MC68HC705RC16 — Rev. 3.0

Resets

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 (tcyc) 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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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