M306H7MG-XXXFP Datasheet, PDF (41/329 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER with DATA ACQUISITION CONTROLLER

M306H7MG-XXXFP/MC-XXXFP/FGFP
4. CLOCK GENERATION CIRCUIT
4.5 System Clock Protective Function
When the main clock is selected for the CPU clock source, this function disables the clock against modifications 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, CM05, and CM07 bits in CM0 register
• CM10, CM11 bits in CM1 register
Before the system clock protective function can be used, the following register settings must be made while the
CM05 bit of CM0 register is “0” (main clock oscillating) and CM07 bit is “0” (main clock selected for the CPU
clock source):
(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.2.10 Oct 25, 2006 Page 41 of 326
REJ03B0152-0210