UPD17708 datasheet(330/356 Pages) NEC

330 / 356 page

330

µPD17704, 17705, 17707, 17708, 17709

21.7.3 Power failure detection by RAM judgment method

By the RAM judgment method, a power failure is detected by judging whether the contents of the data memory

at a specific address are a specific value when the device has been reset.

An example of a program that detects a power failure by RAM judgment method is shown below.

By the RAM judgment method, a power failure is detected by comparing an “undefined” value and a “specific” value

because the contents of the data memory are “undefined” on application of supply voltage VDD.

Therefore, a power failure may be judged by mistake by this method as described in 21.7.4 Cautions on power

failure detection by RAM judgment method.

Example Program example of power failure detection by RAM judgment method

M012

MEM

0.12H

M034

MEM

0.34H

M056

MEM

0.56H

M107

MEM

1.07H

M128

MEM

1.28H

M16F

MEM

1.6FH

DATA0

DAT

1010B

DATA1

DAT

0101B

DATA2

DAT

0110B

DATA3

DAT

1001B

DATA4

DAT

1100B

DATA5

DAT

0011B

START:

SET2

CMP, Z

SUB

M012, #DATA0

; If M012 = DATA0, and

SUB

M034, #DATA1

; M034 = DATA1, and

SUB

M056, #DATA2

; M056 = DATA2, and

BANK1

SUB

M107, #DATA3

; M107 = DATA3, and

SUB

M128, #DATA4

; M128 = DATA4, and

SUB

M16F, #DATA5

; M16F = DATA5,

BANK0

SKF1

BACKUP

; branches to BACKUP

; INITIAL:

Initial processing

MOV

M012, #DATA0

MOV

M034, #DATA1

MOV

M056, #DATA2

BANK1

MOV

M107, #DATA3

MOV

M128, #DATA4

MOV

M16F, #DATA5

MAIN

BACKUP:

Backup processing

MAIN:

Main processing

UPD17708 Datasheet(PDF) 330 Page - NEC

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