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M16C/28 Group
Under development Preliminary specification
Specifications in this manual are tentative and subject to change.
7. Clock Generation Circuit
Rev.0.60 2004.02.01
page 44 of N
REJ09B0047-0060Z
7.6.1.6 Ring Oscillator Mode
The selected ring oscillator clock divided by 1 (undivided), 2, 4, 8 or 16 provides the CPU clock. The
ring 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 ring oscillator frequency can be selected
using the ring oscillator control register (ROCR:025C16) bits 0 to 3. See Figure.7.4 for details. 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 Ring Oscillator Low Power Dissipation Mode
The main clock is turned off after being placed in ring oscillator mode. The CPU clock can be selected
as in the ring oscillator mode. The ring 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.
1(Note 1)
Modes
CM2 register
CM21
CM1 register
CM11
CM17, CM16
CM0 register
CM07
CM06
CM05
CM04
PLL operation mode
01
002
00
High-speed mode
0
002
00
0
Medium-
speed
mode
00
012
00
0
00
102
00
0
divided by 2
00
0
1
0
00
112
00
0
Low-speed mode
1
0
1
Low power dissipation mode
11
Ring
oscillator
mode
(Note 3)
1
divided by 4
divided by 8
divided by 16
Ring oscillator low power
dissipation mode
Note 1: When the CM05 bit is set to ì1 (main clock turned off) in low-speed mode, the mode goes to low power
dissipation mode and CM06 bit is set to ì1 (divided by 8 mode) simultaneously .
Note 2: The divide-by-n value can be selected the same way as in ring oscillator mode.
0
1012
00
0
1102
00
0
11
0
1112
00
0
1002
00
0
(Note 2)
divided by 2
divided by 4
divided by 8
divided by 16
divided by 1
1(Note 1)
(Note 2)
1
Note 3: Variable ring oscillator frequency can be any of those described in the section "Variable Ring Oscillator Mode".
0
7.6.2 Wait Mode
In wait mode, the CPU clock is turned off, so are the CPU (because operated by the CPU clock) and the
watchdog timer. However, if the PM22 bit of PM2 register is “1” (ring oscillator clock for the watchdog
timer count source), the watchdog timer remains active. Because the main clock, sub clock, ring oscillator
clock and PLL 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,
f8SIO, f32SIO and fAD clocks are turned off when 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 = “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).
7.6.2.3 Pin Status During Wait Mode
The I/O port pins retain their status held just prior to wait mode.
Table 7.6.1.1. Setting Clock Related Bit and Modes