M16C29 Datasheet, PDF (80/499 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/Tiny SERIES

M16C/29 Group
7. Clock Generation Circuit
7.3 On-chip Oscillator Clock
This clock is supplied by a variable on-chip oscillator. This clock is used as the clock source for the CPU
and peripheral function clocks. In addition, if the PM22 bit in the PM2 register is 1 (on-chip oscillator clock
for the watchdog timer count source), this clock is used as the count source for the watchdog timer (Refer
to 10. Watchdog Timer • Count source protective mode”).
After reset, the on-chip oscillator clock divided by 16 is used for the CPU clock. It can also be turned on by
setting the CM21 bit in the CM2 register to 1 (on-chip oscillator clock), and is used as the clock source for
the CPU and peripheral function clocks. If the main clock stops oscillating when the CM20 bit in the CM2
register is 1 (oscillation stop, re-oscillation detection function enabled) and the CM27 bit is 1 (oscillation
stop, re-oscillation detection interrupt), the on-chip oscillator automatically starts operating, supplying the
necessary clock for the MCU.
7.4 PLL Clock
The PLL clock is generated from the main clock by a PLL frequency synthesizer. This clock is used as the
clock source for the CPU and peripheral function clocks. After reset, the PLL clock is turned off. The PLL
frequency synthesizer is activated by setting the PLC07 bit to 1 (PLL operation). When the PLL clock is
used as the clock source for the CPU clock, wait tsu(PLL) for the PLL clock to be stable, and then set the
CM11 bit in the CM1 register to 1.
Before entering wait mode or stop mode, be sure to set the CM11 bit to 0 (CPU clock source is the main
clock). Furthermore, before entering stop mode, be sure to set the PLC07 bit in the PLC0 register to 0 (PLL
stops). Figure 7.10 shows the procedure for using the PLL clock as the clock source for the CPU.
The PLL clock frequency is determined by the equation below.
PLL clock frequency=f(XIN) X (multiplying factor set by bits PLC02 to PLC00 in the PLC0 register
(However, 10 MHz ≤ PLL clock frequency ≤ 20 MHz)
Bits PLC02 to PLC00 can be set only once after reset. Table 7.2 shows the example for setting PLL clock
frequencies.
Table 7.2 Example for Setting PLL Clock Frequencies
XIN
PLC02
(MHz)
PLC01
PLC00
Multiplying factor
10
0
0
1
2
5
0
1
0
4
NOTE:
1. 10MHz ≤ PLL clock frequency ≤ 20MHz.
PLL clock
(MHz)⁽¹⁾
20
Rev. 1.12 Mar.30, 2007
REJ09B0101-0112
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