NEC uPD78P078 - Manual (Page 565)

565
CHAPTER 26 ROM CORRECTION
26.5 ROM Correction Example
The example of ROM correction when the instruction at address 1000H “ADD A, #1” is changed to “ADD A, #2”
is as follows.
Figure 26-8. ROM Correction Example
(1) Branches to address F7FDH when the preset value 1000H in the correction address register matches the
fetch address value after the main program is started.
(2) Branches to any address (address F702H in this example) by setting the entire-space branch instruction
(BR !addr16) to address F7FDH with the main program.
(3) Returns to the internal ROM program after executing the substitute instruction ADD A, #2.
ADD A, #2
BR !1002H
BR !F702H
ADD A, #1
MOV B, A
0000H
0080H Program start
1000H
1002H
Internal ROM Internal expansion RAM
0000H
F702H
F7FDH
F7FFH
(1)
(2)
(3)