M16C62_M Datasheet, PDF (321/615 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/60 SERIES

Protect
Mitsubishi microcomputers
M16C / 62A Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
2.1.2 Protect Operation
The 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 system
clock 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 clock
control 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. Make
changes in input/output and SI/Oi control register (i=3,4) immediately after the instruction that
sets “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 being
executed.
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