Clock Generation Circuit
53
Mitsubishi microcomputers
M16C / 62P Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
development
Preliminary Specifications Rev.1.0
Specifications in this manual are tentative and subject to change.
System clock control register 0 (Note 1)
Symbol
CM0
Address
0006
16
After reset
01001000
2
Bit name
Function
Bit symbol
b7
b6
b5
b4
b3
b2
b1
b0
7
0 1 : f
C
output
1 0 : f
8
output
1 1 : f
32
output
0 : Do not stop peripheral function clock in wait mode
1 : Stop peripheral function clock in wait mode (Note 8)
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 (Note 10)
X
CIN
-X
COUT
drive capacity
select bit (Note 2)
Port X
C
select bit
(Note 2)
0 : LOW
1 : HIGH
0 : I/O port P8
6
, P8
7
1 : X
CIN
-X
COUT
generation function(Note 9)
0 : On
1 : Off (Note 4, Note5)
Main clock stop bit
(Notes 3, 10, 12, 13)
Main clock division select
bit 0 (Notes 7, 13)
0 : CM16 and CM17 valid
1 : Division by 8 mode
System clock select bit
(Notes 6, 10, 11, 12)
0 : Main clock, PLL clock, or ring oscillator clock
1 : Sub-clock
Note 1: Write to this register after setting the PRC0 bit of PRCR register to “1” (write enable).
Note 2: The CM03 bit is set to “1” (high) when the CM04 bit is set to “0” (I/O port) or the microcomputer goes to a stop mode.
Note 3: This bit is provided to stop the main clock when the low power dissipation mode or ring oscillator low power dissipation mode
is selected. This bit cannot be used for detection as to whether the main clock stopped or not. To stop the main clock, the
following setting is required:
(1) Set the CM07 bit to “1” (Sub-clock select) or the CM21 bit of CM2 register to “1” (Ring oscillator select) with the sub-clock
stably oscillating.
(2) Set the CM20 bit of CM2 register to “0” (Oscillation stop, re-oscillation detection function disabled).
(3) Set the CM05 bit to “1” (Stop).
Note 4: During external clock input, only the clock oscillation buffer is turned off and clock input is accepted.
Note 5: When CM05 bit is set to “1, the X
OUT
pin goes “H”. Furthermore, because the internal feedback resistor remains connected,
the X
IN
pin is pulled “H” to the same level as X
OUT
via the feedback resistor.
Note 6: After setting the CM04 bit to “1” (X
CIN
-X
COUT
oscillator function), wait until the sub-clock oscillates stably before switching
the CM07 bit from “0” to “1” (sub-clock).
Note 7: When entering stop mode from high or middle speed mode, ring oscillator mode or ring oscillator low power mode, the CM06
bit is set to “1” (divide-by-8 mode).
Note 8: The f
C32
clock does not stop. During low speed or low power dissipation mode, do not set this bit to “1” (peripheral clock
turned off when in wait mode).
Note 9: To use a sub-clock, set this bit to “1”. Also make sure ports P8
6
and P8
7
are directed for input, with no pull-ups.
Note 10: When the PM21 bit of PM2 register is set to “1” (clock modification disable), writing to the CM02, CM05, and CM07 bits has
no effect.
Note 11: If the PM21 bit needs to be set to “1”, set the CM07 bit to “0”(main clock) before setting it.
Note 12: To use the main clock as the clock source for the CPU clock, follow the procedure below.
(1) Set the CM05 bit to “0” (oscillate).
(2) Wait until td(M-L) elapses or the main clock oscillation stabilizes, whichever is longer.
(3) Set the CM11, CM21 and CM07 bits all to “0”.
Note 13: If the CM05 bit is set to “1” (main clock turned off) in low speed mode, the CM06 bit is set to “1” (divide-by-8 mode) and the
CM15 bit is set to “1” (drive capability high). Avoid changing the CM06 bit in low power dissipation mode.
During ring oscillator mode, the CM06 and CM15 bits do not change even if the CM05 bit is set to “1”. During ring oscillator
low power dissipation mode, the divide-by-n value can be selected using the CM06 and CM17 to CM16 bits. To return to
high or middle speed mode, however, set the CM06 bit to “1” and the CM15 bit to “1” before selecting the desired mode.
RW
RW
RW
RW
RW
RW
RW
RW
RW
Figure 1.9.2. CM0 Register