Rom Correction Example - NEC PD78052 User Manual

25.5 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.
0000H
0080H
1000H
1002H
EFFFH
(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.
CHAPTER 25 ROM CORRECTION
Figure 25-8. ROM Correction Example
Internal ROM
Program start
(3)
ADD A, #1
MOV B, A
(1)
Internal expansion RAM
F400H
F702H ADD A, #2
BR !1002H
F7FDH
BR !F702H
F7FFH
(2)
543