Mitsubishi microcomputers
M16C / 6N0 / 6N1 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
40
Figure 1.10.4. Clock control registers 0 and 1
Figure 1.10.4 shows the system clock control registers 0 and 1.
System clock control register 0 (Note 1)
Symbol
Address
When reset
CM0
000616
4816
Bit name
Function
Bit symbol
b7
b6
b5
b4
b3
b2
b1
b0
0 0 : I/O port P57
0 1 : fC output
1 0 : f8 output
1 1 : f32 output
b1 b0
CM07
CM05
CM04
CM03
CM01
CM02
CM00
CM06
Clock output function
select bit
(Valid only in single-chip
mode)
WAIT peripheral function
clock stop bit
0 : Do not stop peripheral function clock in wait mode
1 : Stop peripheral function clock in wait mode (Note 8)
XCIN-XCOUT drive capacity
select bit (Note 2)
0 : LOW
1 : HIGH
Port XC select bit
0 : I/O port
1 : XCIN-XCOUT generation (Note 9)
Main clock (XIN-XOUT)
stop bit (Note 3, 4, 5, 10)
0 : On
1 : Off
Main clock division select
bit 0 (Note 7)
0 : CM16 and CM17 valid
1 : Division by 8 mode
System clock select bit
(Note 6)
0 : XIN, XOUT
1 : XCIN, XCOUT
System clock control register 1 (Note 1)
Symbol
Address
When reset
CM1
000716
2016
Bit name
Function
Bit symbol
b7
b6
b5
b4
b3
b2
b1
b0
CM10
All clock stop control bit
(Note4)
0 : Clock on
1 : All clocks off (stop mode)
Note 1: Set bit 0 of the protect register (address 000A16) to "1" before writing to this register.
Note 2: This bit changes to "1" when shifting from high-speed/medium-speed mode to stop mode and at a reset. When
shifting from low-speed/low power dissipation mode to stop mode, the value before stop mode is retained.
Note 3: Can be selected when bit 6 of the system clock control register 0 (address 000616) is "0". If "1", division mode is
fixed at 8.
Note 4: If this bit is set to "1", XOUT turns "H", and the built-in feedback resistor is cut off. XCIN and XCOUT turn high-
impedance state.
CM15
XIN-XOUT drive capacity
select bit (Note 2)
0 : LOW
1 : HIGH
W
R
W
R
CM16
CM17
Reserved bits
Must always be set to
"0"
Main clock division
select bit 1 (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
Note 1: Set bit 0 of the protect register (address 000A16) to "1" before writing to this register.
Note 2: Changes to "1" when shiffing to stop mode and at a reset.
Note 3: When entering the low power dissipation mode and the ring oscillator mode, main clock stops by using this bit.
To stop the main clock, when the sub clock oscillation is stable, set system clock select bit (CM07) to "1" be-
fore setting this bit to "1".
Note 4: When inputting external clock, only clock oscillation buffer is stopped and clock input is acceptable.
Note 5: If this bit is set to "1", XOUT turns "H". The built-in feedback resistor remains being connected, so XIN turns
pulled up to XOUT ("H") via the feedback resistor.
Note 6: Set port XC select bit (CM04) to "1" and stabilize the sub clock oscillating before setting this bit from "0" to "1".
Do not write to both bits at the same time. And also, set the main clock stop bit (CM05) to "0" and stabilize the
main clock oscillating before setting this bit from "1" to "0".
Note 7: This bit changes to "1" when shifting from high-speed/medium-speed mode to stop mode and at a reset. When
shifting from low-speed/low power dissipation mode to stop mode, the value before stop mode is retained.
Note 8: fC32 is not included. Do not set to "1" when using low-speed or low power dissipation mode.
Note 9: When the XCIN/XCOUT is used, set ports P86 and P87 as the input ports without pull-up.
Note10: Setting this bit to "1" disables the main clock buffer. If the oscillation is generated by a quartz crystal or ceramic os-
cillator, oscillation stops. To avoid stopping the MCU, set CM07 to "1" or CM21 to "1" prior to setting this bit to "1".
Clock Generating Circuit