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n Operations of ROM correction
When the program counter indicates the same address as the ROM correction address register, the INT9
instruction will be executed. By processing the INT9 interrupt service routine, the ROM correction function
can be achieved.
There are two address registers, in each containing a compare enable bit. When the address register and
the program counter a match, and when the compare enable bit is '1', then the CPU will be forced to execute
INT9 instruction.
Note:
When the address register and the program counter match, the internal data bus content will be
forced to be '01H', so INT9 instruction will be executed. Before changing the content of the ad-
dress register, make sure the compare enable bit is '0'. If it is changed while the compare enable
bit is at '1', there will occur an error.
The ROM correction function is only enabled for internal ROM addresses. The INT9 instruction is
not issued when addresses of the external memory area are set.
ROM CORRECTION
21-5
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