7220 Datasheet, PDF (188/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
5.3 Usage example of ROM correction function (M37221M8/MA-XXXSP)
5.3 Usage example of ROM correction function (M37221M8/MA-XXXSP)
Application example using the ROM correction function is described below. In this example, it is assumed
that the program must be changed by specifications modification after completion of ROM mask. Also,
E²PROM is connected to this system.
5.3.1 Connection example
I²C-BUS
<E²PROM>
Fig. 5.3.1 Connection example
<Microcomputer>
5.3.2 Correction example
The following is an example when 2 addresses (2 blocks) of ROM are corrected.
(1) Correction example 1
Program before correction
Address
Machine
Description style
instructions
E120
A900
LDA #00H
E122
E123
3A
8D1101
INC A
STA 0111H
E126
60
RTS
Address
(block 1)
02C0
02C2
02C3
02C6
02C7
02CA
Correction program
Machine
Description style
instructions
A980
LDA #80H
1A
DEC A
8D1201
1A
STA 0112H
DEC A
8D1301
4C26E1
DEC 0113H
JMP E126H Π(See note)
Note: In Œ, E126H is specified as the return destination address of JMP.
In this example, since the instruction at the return destination address is RTS,
even if RTS is used instead of JMP, the operation is the same as that of JMP.
As a result, the number of bytes is reduced.
Fig. 5.3.2 Correction example (1)
7220 Group User’s Manual
5-15