Software Trap Technology-EEWORLD

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When the CPU is disturbed, it often treats some operands as instruction codes to execute, causing confusion in program execution. The main methods in A51 are as follows:
1. Interrupt vector area
ORG 0000H
START: LJMP MAIN
LJMP INT0
NOP
NOP
LJMP ERR ; Trap
LJMP TOINT
NOP
NOP
LJMP ERR ; Trap
- - - -
ORG 0040H
ERR:
-----------

2. In the table area
At the end of the table area, arrange a 5-byte trap
TABEL1:
DB ------------
DB ------------
NOP
NOP
LJMP ERR
3. In the unused ROM space
The unused ROM space is usually all 0FFH, which is the single-byte instruction "MOV R7, A" for 51. Once the program jumps to this area, it will fall straight down. Generally, software traps are added at some fixed addresses to capture the jumping program.
ORG 6000H
NOP
NOP
LJMP ERR
ORG 7FFBH
NOP
NOP
LJMP ERR
4. After the subroutine
XXXX:
;;;;;;;;;;;
;;;;;;;;;;
RET
NOP
NOP
LJMP ERR

And at the breakpoints of some long jumps...

Note: The ERR subroutine should reset the stack and other initialization parameters, but some data in the RAM area can be retained.

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