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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 34 of N
REJ09B0047-0060Z
System clock control register 1 (Note 1)
Symbol
Address
After reset
CM1
000716
001000002
Bit
name
Function
Bit symbol
b7
b6
b5
b4
b3
b2
b1
b0
CM10
All clock stop control bit
(Notes 4, 6)
0 : Clock on
1 : All clocks off (stop mode)
Note 1: Write to this register after setting the PRC0 bit of PRCR register to “1” (write enable).
Note 2: When entering stop mode from high or middle speed mode, or when the CM05 bit is set to “1” (main clock turned off) in low
speed mode, the CM15 bit is set to “1” (drive capability high).
Note 3: Effective when the CM06 bit is “0” (CM16 and CM17 bits enable).
Note 4: If the CM10 bit is “1” (stop mode), XOUT goes “H” and the internal feedback resistor is disconnected. The XCIN and XCOUT
pins are placed in the high-impedance state. When the CM11 bit is set to “1” (PLL clock), or the CM20 bit of CM2 register is
set to “1” (oscillation stop, re-oscillation detection function enabled), do not set the CM10 bit to “1”.
Note 5: After setting the PLC07 bit in PLC0 register to “1” (PLL operation), wait until Tsu (PLL) elapses before setting the CM11 bit to
“1” (PLL clock).
Note 6: When the PM21 bit of PM2 register is set to “1” (clock modification disable), writing to the CM10, CM011 bits has no effect.
When the PM22 bit of PM2 register is set to “1” (watchdog timer count source is ring oscillator clock), writing to the CM10 bit
has no effect.
Note 7: Effective when CM07 bit is “0” and CM21 bit is “0” .
CM15
XIN-XOUT drive capacity
select bit (Note 2)
0 : LOW
1 : HIGH
RW
CM16
CM17
Reserved bit
Must set to
“0”
Main clock division
select bits
(Note 3)
0 0 : No division mode
0 1 : Division by 2 mode
1 0 : Division by 4 mode
1 1 : Division by 16 mode
b7 b6
0
00
CM11
System clock select bit 1
(Notes 6, 7)
0 : Main clock
1 : PLL clock (Note 5)
RW
(b4-b2)
Figure 7.3. CM1 Register
Figure 7.4. ROCR Register
b7
b6
b5
b4
b3
b2
b1
b0
RW
ROCR0
ROCR1
Ring Oscillator Control register (Note 1)
Symbol
Address
After reset
ROCR
025C16
000001012
Bit name
Function
Bit symbol
Frequency select bits
RW
Reserved bit
(b7-b4)
Must set to “0”
RW
00
0 0 : f1 (ROC)
0 1 : f2 (ROC)
1 0 : not supported
1 1 : f3 (ROC)
b1 b0
ROCR2
ROCR3
Divider select bits
RW
0 0 : not supported
0 1 : divide by 2
1 0 : divide by 4
1 1 : divide by 8
b3 b2
Note 1 : Write to this register after setting the PRC0 bit of PRCR register to "1" (write enable).