M16C6S_09 Datasheet, PDF (44/208 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

M16C/6S Group
Clock Generation Circuit
System Clock Protective Function
When the main clock is selected for the CPU clock source, this function disables the clock against modifica-
tions in order to prevent the CPU clock from becoming halted by run-away.
If the PM21 bit of PM2 register is set to “1” (clock modification disabled), the following bits are protected
against writes:
• CM02 bit in CM0 register
• CM10, CM11 bits in CM1 register
• CM20 bit in CM2 register
Before the system clock protective function can be used, the following register settings must be made:
(1) Set the PRC1 bit of PRCR register to “1” (enable writes to PM2 register).
(2) Set the PM21 bit of PM2 register to “1” (disable clock modification).
(3) Set the PRC1 bit of PRCR register to “0” (disable writes to PM2 register).
Do not execute the WAIT instruction when the PM21 bit is “1”.
Rev.5.01 Dec 10, 2009 page 44 of 201
REJ03B0014-0501