M16C User Manual.pdf

Functions To Inhibit Rewriting (Flash Memory Version)Mitsubishi microcomputersM16C / 62 GroupSINGLE-CHIP 16-BIT CMOS MICROCOMPUTERFunctions To Inhibit Rewriting Flash Memory VersionTo prevent the contents of the flash memory version from being read out or rewritten easily, the deviceincorporates a ROM code protect function for use in parallel I/O mode and an ID code check function foruse in standard serial I/O mode.ROM code protect functionThe ROM code protect function reading out or modifying the contents of the flash memory version byusing the ROM code protect control address (0FFFFF16) during parallel I/O mode. Figure 1.29.9 showsthe ROM code protect control address (0FFFFF16). (This address exists in the user ROM area.)If one of the pair of ROM code protect bits is set to 0, ROM code protect is turned on, so that the contentsof the flash memory version are protected against readout and modification. ROM code protect is implementedin two levels. If level 2 is selected, the flash memory is protected even against readout by ashipment inspection LSI tester, etc. When an attempt is made to select both level 1 and level 2, level 2 isselected by default.If both of the two ROM code protect reset bits are set to “00,” ROM code protect is turned off, so that thecontents of the flash memory version can be read out or modified. Once ROM code protect is turned on,the contents of the ROM code protect reset bits cannot be modified in parallel I/O mode. Use the serial I/O or some other mode to rewrite the contents of the ROM code protect reset bits.ROM code protect control addressb7 b6 b5 b4 b3 b2 b1 b0Symbol Address When resetROMCP 0FFFFF16 FF16Bit symbol Bit nameFunctionReserved bit Always set this bit to 1.ROMCP2b3 b2ROM code protect level2 set bit (Note 1, 2) 00: Protect enabled01: Protect enabled10: Protect enabled11: Protect disabledROMCRROMCP1ROM code protect resetbit (Note 3)ROM code protect level1 set bit (Note 1)b5 b400: Protect removed01: Protect set bit effective10: Protect set bit effective11: Protect set bit effectiveb7 b600: Protect enabled01: Protect enabled10: Protect enabled11: Protect disabledNote 1: When ROM code protect is turned on, the on-chip flash memory is protected againstreadout or modification in parallel input/output mode.Note 2: When ROM code protect level 2 is turned on, ROM code readout by a shipmentinspection LSI tester, etc. also is inhibited.Note 3: The ROM code protect reset bits can be used to turn off ROM code protect level 1 andROM code protect level 2. However, since these bits cannot be changed in parallel input/output mode, they need to be rewritten in serial input/output or some other mode.Figure 1.29.9. ROM code protect control address250