M32C80 Datasheet, PDF (329/352 Pages) Renesas Technology Corp – 16/32-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M32C/80 SERIES

M32C/80 Group
24. Precautions (Clock Generation Circuit)
24.4 Clock Generation Circuit
24.4.1 CPU Clock
• When the CPU operating frequency is 24 MHz or more, use the following procedure for better EMC
(Electromagnetic Compatibility) performance.
1) Oscillator connected between the XIN and XOUT pins, or external clock applied to the
XIN pin, has less than 24 MHz frequency.
2) Use the PLL frequency synthesizer to multiply the main clock.
24.4.2 Sub Clock
Set the CM03 bit to "0" (XCIN-XCOUT drive capacity "LOW") when selecting the sub clock (XCIN-XCOUT) as
the CPU clock, or Timer A or Timer B count source (fC32).
24.4.2.1 Sub Clock Oscillation
When oscillating the sub clock, set the CM04 bit in the CM0 register to "1" (XCIN-XCOUT oscillation
function) after setting the CM07 bit in the CM0 register to "0" (clock other than sub clock) and the
CM03 bit to "1" (XCIN-XCOUT drive capacity "HIGH"). Set the CM03 bit to "0" after sub clock oscillation
stabilizes.
Set the sub clock as the CPU clock, or Timer A or Timer B count source (fC32) after the above settings
are completed.
24.4.2.2 Using Stop Mode
When the microcomputer enters stop mode, the CM03 bit is automatically set to "1" (XCIN-XCOUT drive
capacity "HIGH"). Use the following procedure to select the main clock as the CPU clock when enter-
ing stop mode.
1) Set the CM17 bit in the CM1 register to "0" (main clock).
2) Set the CM21 bit in the CM2 register to "0" (clock selected by the CM17 bit).
3) Set the CM07 bit in the CM0 register to "0" (clock selected by the CM21 bit divided by the MCD
register setting).
After exiting stop mode, wait for the sub clock oscillation to stabilize. Then set the CM03 bit to "0" and
the CM07 bit to "1" (sub clock).
24.4.2.3 Oscillation Parameter Matching
If the sub slock oscillation parameters have only been evaluated with the drive capacity "HIGH", the
parameters should be reevaluated for drive capacity "LOW".
Contact your oscillator manufacturer for details on matching parameters.
Rev. 1.00 Nov. 01, 2005 ^{Page 310} of 330
REJ09B0271-0100