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CHAPTER 21 ROM CORRECTION FUNCTION
21.1
Overview of the ROM Correction Function
An instruction code to be read by the CPU is replaced forcibly with an INT9 instruction
code (01
) when the corresponding address is equal to the value set in a program
H
address detect register. A program patch application function can be implemented by
processing with the INT #9 interrupt routine.
■ Program Address Detection Registers (× 2)
There are two program address detection registers (PADR0/PADR1), each is provided with an interrupt
enable bit and interrupt flag.
■ ROM Correction Interrupts
When the interrupt enable bit is "1", the value set in the program address detection register is compared
with the address. If the value matches the address, "1" is set in the interrupt flag bit and the instruction code
to be read to the CPU, is forcibly replaced with an INT9 instruction code.
The interrupt flag bit is cleared to "0" by writing "0" to it using an instruction.
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