User’s Manual U13850EJ4V0UM
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CHAPTER 17 ROM CORRECTION FUNCTION
17.1 General
The ROM correction function provided in the V850/SB1 and V850/SB2 is a function that replaces part of a
program in the mask ROM with a program in the internal RAM.
First, the instruction of the address where the program replacement should start is replaced with the JMP r0
instruction and the program is instructed to jump to 00000000H. The correction request register (CORRQ) is then
checked. At this time, if the CORRQn flag is set to 1, program control shifts to the internal RAM after jumping to the
internal ROM area by an instruction such as a jump instruction.
Instruction bugs found in the mask ROM can be avoided, and program flow can be changed by using the ROM
correction function.
Up to four correction addresses can be specified.
Cautions 1. The ROM correction function cannot be used for the data in the internal ROM; it can only be
used for instruction codes. If ROM correction is carried out on data, that data will replace the
instruction code of the JMP r0 instruction.
2. ROM correction for the instructions that access the registers CORCN, CORRQ, or CORAD0 to
CORAD3 is prohibited.
Figure 17-1. Block Diagram of ROM Correction
ROM
(1 MB area)
Instruction address bus
S Q
R
Correction address
register n (CORADn)
Comparator
Correction control register
(CORCNn bit)
JMP r0 instruction
generation
Instruction
replacement
Instruction data
bus
Correction request
register (CORRQn bit)
0 clear instruction
Remark
n = 0 to 3