UPD17073 NEC, UPD17073 Datasheet - Page 192

• Manufacturer Part Number: UPD17073
• Description: 4-BIT SINGLE-CHIP MICROCONTROLLER WITH HARDWARE FOR DIGITAL TUNING SYSTEM
• Manufacturer: NEC

M2 are “1H” and “2H”, respectively.
“12H”, and if they are the same, the ordinary processing is performed.
<3>.
0000H without <3> executed.
192
Suppose the security code is “12H” in this example. Then the contents of the data memory addresses M1 and
When the CE reset is effected at this time, the contents of the key input in <1> are compared with the security code
When the security code is changed by the main processing, the new code is rewritten to M1 and M2 in <2> and
Suppose the security code is changed to “34H”. Then “3H” and “4H” are written to M1 and M2 in <2> and <3>.
However, if the CE reset happens to occur when <2> has been executed, the program is started from address
Consequently, the security code is changed to “32H”, which is not intended, and security cannot be released.
In this case, use the program shown in Example 2.
Example 1.
R1
R2
R3
R4
M1
M2
START:
MAIN:
ERROR:
MEM
MEM
MEM
MEM
MEM
MEM
SET2
SUB
SUB
SKT1
BR
ST
ST
BR
Key input processing
Key input processing
R1
R2
R3
R4
Does not operate
Key C contents
Key D contents
Key B contents
0.01H
0.02H
0.03H
0.04H
Key A contents
CMP, Z
Z
ERROR
M1, R3
M2, R4
MAIN
0.11H
0.12H
R1, M1
R2, M2
; <1>
; <2>
; <3>
; 1st digit of input data of security code
; 2nd digit of input data of security code
; Data of 1st digit when security code is changed
; Data of 2nd digit when security code is changed
; 1st digit of current security code
; 2nd digit of current security code
; Waits for key input of
; security code
; Substitutes contents of pressed code into R1 and R2
; Compares security code with input data
; Input data is different from security code
; Security code rewriting mode
; Substitutes contents of
; pressed key into R3 and R4
; Rewrites security code
PD17072,17073