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Chapter 2 CPU Basics
II - 30
ROM Correction
2-7 ROM Correction
2-7-1 Overview
This LSI can correct and change max. 3 parts in a program on mask ROM with ROM correction function.
The correct program is read from the external to the RAM space by using the external EEPROM or by
using the serial transmission. This function is valid to the system with the external EEPROM.
2-7-2 Correction Sequence
Program is corrected as following steps.
(1) The instruction execution address is compared to the correction address.
(2) Program counter is branched indirectly to the RAM address (the head address of the correct pro-
gram) stored to the RC vector table (RCnV(L), RCnV(H)), after matching the above addresses.
This instruction needs 6 cycle.
(3) The corrected program at the RAM area is executed.
(4) Program counter is branched back to the program at ROM area.
NG Instruction
the head address to be corrected
recover
When a match occurs, the program
counter branches indirectly to
the start address of the correct program.
internal ROM internal RAM
label 2_
Correct program
JMP label2_
RCnV(L)
RCnV(H)
label 1
Development data
from the external EEPROM
Figure 2-7-1 ROM Correction