M16C User Manual.pdf

ProtectMitsubishi microcomputersM16C / 62 GroupSINGLE-CHIP 16-BIT CMOS MICROCOMPUTER2.1.2 Protect OperationThe following explains the protect operation. Figure 2.1.2 shows the set-up procedure.Operation (1) Setting “1” in the write-enable bit of system clock control registers 0 and 1 causes systemclock control register 0 and system clock control register 1 to be in write-enabled state.(2) The contents of system clock control register 0 and that of system clock control register 1 are changed.(3) Setting “0” in the write-enable bit of system control registers 0 and 1 causes system clockcontrol register 0 and system control register 1 to be in write-inhibited state.(4) To change the contents of processor mode register 0 and that of processor mode register 1,follow the same steps as in dealing with system clock control registers.(5) The write-enable bit of port 9 direction register and SI/Oi control register (i=3,4) goes to “0”when the next write instruction is executed after write-enabled state is readied. Makechanges in input/output and SI/Oi control register (i=3,4) immediately after the instruction thatsets “1” in the write-enable bit of port P9 direction register and SI/Oi control register(i=3,4)(avoid causing an interrupt). Also take measures to prevent DMA transfer from beingexecuted.278