M32C80 Datasheet, PDF (99/352 Pages) Renesas Technology Corp – 16/32-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M32C/80 SERIES

M32C/80 Group
8. Clock Generation Circuit
8.6 System Clock Protect Function
The system clock protect function prohibits the CPU clock from changing clock sources when the main
clock is selected as the CPU clock source. This prevents the CPU clock from stopping the program crash.
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 CM17 bit in the CM1 register
• The CM20 bit in the CM2 register
• All bits in the PLC0 and PLC1 registers
The CPU clock continues running when the WAIT instruction is executed.
To use the system clock protect function, set the CM05 bit in the CM0 register to "0" (main clock oscillation)
and CM07 bit to "0" (main clock as BCLK clock source) and follow the procedure below.
(1) Set the PRC1 bit in the PRCR register to "1" (write enabled).
(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 disabled).
When the PM21 bit is set to "1", do not execute the WAIT instruction.
Rev. 1.00 Nov. 01, 2005 Page 80 of 330
REJ09B0271-0100