Engineering Bulletin

EB413

8

MOTOROLA

this in turn can result in the HC05 running away by incorrectly reading

ROM or RAM.

The best solution to such problems is the use of a low-voltage reset

circuit (such as the MC34064 and MC34164 devices) which force reset

Figure 2. MC34064 Low-Voltage Reset Device Application

It is often assumed that EEPROM is erased or incorrectly written during

power up, but normally it is during power down that the erroneous

EEPROM activity occurs.

NOTE:

The power-down voltage decay is often slow and the lack of any low-

voltage reset device could allow the MCU to run at too high a frequency

several erases and writes to EEPROM).

Battery Backup

The usual purpose for battery backup operation is to avoid resetting the

MCU when the main power is removed. There comes a point though,

when the battery also fails and this can cause the voltage on the system

to drop very gradually. To save the battery from damaging itself, it is

usual to have low-voltage detection circuits that force a system reset as

the power drops below a critical level. In these circumstances, it is often

necessary to save the current status of the MCU before the reset occurs

and so it is likely the system will first warn the MCU of the pending reset.

+5 V

20 k

Ω

MCU

RESET

MC34064

RESET PIN

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com