UPD17015 datasheet(97/120 Pages) NEC

97 / 120 page

µPD17015

Example 1

MEM

0.01H

; First digit of security code keyed in

MEM

0.02H

; Second digit of security code keyed in

MEM

0.03H

; Data of the first digit when the security code is

changed

MEM

0.04H

; Data of the second digit when the security code is

changed

MEM

0.11H

; First digit of the current security code

MEM

0.12H

; Second digit of the current security code

START:

Key-in processing

; Security code input wait mode

← Contents of key A

; Assigns the contents of the pressed keys to R1

← Contents of key B

; and R2

SET2

CMP, Z

; 1

; Compares the input data with the security code.

SUB

R1, M1

SUB

R2, M2

SKT1

ERROR

; Detects that the input data does not match the

; security code.

MAIN:

Key-in processing

; Security code rewrite mode

← Contents of key C

; Assigns the contents of the pressed keys to R3

← Contents of key D

; and R4.

M1, R3

; 2

; Rewrites the security code.

M2, R4

; 3

ERROR:

MAIN

Stops the operation.

Suppose, in the program in example 1, that the security code is 12H. The contents of data memory M1 and M2

are 1H and 2H, respectively.

When a CE reset occurs, the key input is compared with security code 12H in 1 . If they match, processing is

performed.

If the security code is changed as part of main processing, the new code is written to M1 and M2 in 2 and 3 .

If the security code is changed to 34H, for example, 3H and 4H are written to M1 and M2 in 2 and 3 .

If a CE reset occurs after 2 , the program starts from 0000H, without executing 3 .

The security code is actually changed to 32H, making it impossible to remove the security lock.

If this problem occurs, use a program like that shown in example 2 below:

UPD17015 Datasheet(PDF) 97 Page - NEC

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