Engineering Bulletin

EB413

2

MOTOROLA

Factors which affect reset are:

1. External components attached to the RESET pin

2. Low-voltage reset (LVR) on chip

3. Power-on reset (POR) detection

4. System power-up sequence

5. Watchdog operation

6. Electrically erasable, programmable read-only memory

(EEPROM) on chip

7. Battery backup

8. Device controls to its own power off

9. Partial power loss

10. HC05 clock source

11. Power applied resets

These factors are explained in detail later in this application note. In most

applications several factors apply and so it may be a combination of

these elements of reset functionality that must be considered for the safe

operation of the MCU application.

Almost all HC05 and HC11 devices have an external 4-MHz or 8-MHz

crystal and so it is assumed that the device will have a stable oscillator

stated otherwise). Other possibilities for clock sources are discussed in

HC05 Clock Source.

External Components Attached to the RESET Pin

a relatively small reservoir capacitor (for instance, 1

µF). In this case, the

crystal oscillator will usually start between 5 ms and 10 ms after power

clock. Remember that the 3-V specification normally includes reduced

operating frequency.

Freescale Semiconductor, Inc.

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