UPD17073 NEC, UPD17073 Datasheet - Page 193

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

In this example, the CHANGE flag is set to “1” in <5> before the security code is rewritten in <2> and <3>.
Therefore, the security code is written again in <4> even if the CE reset is effected in <3>.
Example 2.
SECURITY_CHK:
MAIN:
ERROR:
R1
R2
R3
R4
M1
M2
CHANGE FLG
START:
MEM
MEM
MEM
MEM
MEM
MEM
SKT1
BR
ST
ST
CLR1
SET2
SUB
SUB
SKT1
BR
SET1
ST
ST
CLR1
BR
Key input processing
Key input processing
R1
R2
R3
R4
Does not operate
0.01H
0.02H
0.03H
0.04H
0.11H
0.12H
0.13H.0
Key A contents
Key B contents
CHANGE
SECURITY_CHK
M1, R3
M2, R4
CHANGE
CMP, Z
R1, M1
R2, M2
Z
ERROR
Key C contents
Key D contents
CHANGE
M1, R3
M2, R4
CHANGE
MAIN
; <4> ; If CHANGE flag is 1,
; <1> ; Compares security code with input data
; <5> ; Set CHANGE to “1” while security code is rewritten
; <2> ; Rewrites security code
; <3>
; Waits for key input of
; Security code rewriting mode
; 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
; “1” while security code is changed
; security code
; Substitutes contents of pressed code into R1 and R2
; rewrites M1 and M2
; Input data is different from security code
; Substitutes contents of
; pressed key into R3 and R4
; Sets CHANGE flag to “0” after security code is rewritten
PD17072,17073
193