M16C62P_06 Datasheet, PDF (117/421 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/60 SERIES

M16C/62P Group (M16C/62P, M16C/62PT)
10. Clock Generation Circuit
10.5 System Clock Protection Function
The system clock protection function prohibits the CPU clock from changing clock sources when the main clock is
selected the CPU clock source. This prevents the CPU clock from stopping should the program crash. This
function is available when the main clock is selected as the CPU clock source.
When the PM21 bit in the PM2 register is set to “1” (clock change disabled), the following bits cannot be written
to:
• The CM02 bit, CM05 bit and CM07 bit in the CM0 register
• The CM10 bit and CM11 bit in the CM1 register
• The CM20 bit in the CM2 register
• All bits in the PLC0 register
When using the system clock protection function, set the CM05 bit in the CM0 register to “0” (main clock
oscillation) and CM07 bit to “0” (main clock as CPU clock source) and follow the procedure below.
(1) Set the PRC1 bit in the PRCR register to “1” (write enable).
(2) Set the PM21 bit in the PM2 register to “1” (protects the clock).
(3) Set the PRC1 bit in the PRCR register to “0” (write disable).
When the PM21 bit is set to “1,” do not execute the WAIT instruction.
Rev.2.41 Jan 10, 2006 Page 102 of 390
REJ09B0185-0241