Chapter 2 CPU BasicsII - 30 ROM Correction2-7 ROM Correction2-7-1 OverviewThis 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 byusing the serial transmission. This function is valid to the system with the external EEPROM.2-7-2 Correction SequenceProgram 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 correctedrecoverWhen a match occurs, the programcounter branches indirectly tothe start address of the correct program.internal ROM internal RAMlabel 2_Correct programJMP label2_RCnV(L)RCnV(H)label 1Development datafrom the external EEPROMFigure 2-7-1 ROM Correction
