M16C28 Datasheet, PDF (77/423 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/Tiny SERIES

M16C/28 Group (M16C/28, M16C/28B)
7. Clock Generation Circuit
7.6.1.6 On-chip Oscillator Mode
The selected on-chip oscillator clock divided by 1 (undivided), 2, 4, 8 or 16 provides the CPU clock.
The on-chip oscillator clock is also the clock source for the peripheral function clocks. If the sub clock
is on, fC32 can be used as the count source for timers A and B. The on-chip oscillator frequency can be
selected by the ROCR3 to ROCR0 bits in the ROCR registers. When the operation mode is returned
to the high and medium speed modes, set the CM06 bit to “1” (divided by 8 mode).
7.6.1.7 On-chip Oscillator Low Power Dissipation Mode
The main clock is turned off after being placed in on-chip oscillator mode. The CPU clock can be se-
lected as in the on-chip oscillator mode. The on-chip oscillator clock is the clock source for the peripheral
function clocks. If the sub clock is on, fC32 can be used as the count source for Timers A and B.
Table 7.3 Setting Clock Related Bit and Modes
Modes
PLL operation mode
High-speed mode
Medium-
speed
mode
divided by 2
divided by 4
divided by 8
divided by 16
Low-speed mode
Low power dissipation mode
On-chip
oscillator
mode
(3)
divided by 1
divided by 2
divided by 4
divided by 8
divided by 16
On-chip oscillator low power
dissipation mode
CM2 register
CM21
0
0
0
0
0
0
1
1
1
1
1
1
CM1 register
CM11 CM17, CM16
1
002
0
002
0
012
0
102
0
0
112
002
012
102
112
(2)
CM07
0
0
0
0
0
0
1
1
0
0
0
0
0
0
CM0 register
CM06 CM05
0
0
0
0
0
0
0
0
1
0
0
0
0
1⁽¹⁾
1⁽¹⁾
0
0
0
0
0
0
1
0
0
0
(2)
1
CM04
1
1
NOTES:
1. When the CM05 bit is set to "1" (main clock turned off) in low-speed mode, the mo.de goes to low power
dissipation mode and CM06 bit is set to "1" (divided by 8 mode) simultaneously
2. The divide-by-n value can be selected the same way as in on-chip oscillator mode.
3. On-chip oscillator frequency can be any of those described in the section 7.6.1.6 On-chip Oscillator Mode.
7.6.2 Wait Mode
In wait mode, the CPU clock stops running. The CPU and the watchdog timer, operated by the CPU
clock, also stop. However, if the PM22 bit in the PM2 register is “1” (on-chip oscillator clock for the
watchdog timer count source), the watchdog timer remains active. Because the main clock, sub clock and
on-chip oscillator clock all are on, the peripheral functions using these clocks keep operating.
7.6.2.1 Peripheral Function Clock Stop Function
If the CM02 bit is “1” (peripheral function clocks turned off during wait mode), the f1, f2, f8, f32, f1SIO,
f2SIO, f8SIO, f32SIO and fAD clocks stop running in wait mode, with the power consumption reduced that
much. However, fC32 remains on.
7.6.2.2 Entering Wait Mode
The microcomputer is placed into wait mode by executing the WAIT instruction.
When the CM11 bit is set to “1” (CPU clock source is the PLL clock), be sure to clear the CM11 bit to
“0” (CPU clock source is the main clock) before going to wait mode. The power consumption of the
chip can be reduced by clearing the PLC07 bit to “0” (PLL stops).
Rev. 2.00 Jan. 31, 2007 ^{page 57} of 385
REJ09B0047-0200