Mitsubishi microcomputers
M16C / 6N0 / 6N1 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
38
The following paragraphs describe the clocks generated by the clock generating circuit.
(1) Main clock
The main clock is generated by the main clock oscillation circuit. After a reset, the clock is divided by 8 to
the BCLK. The clock can be stopped using the main clock stop bit (bit 5 at address 000616). Stopping the
clock, after switching the operating clock source of CPU to the sub clock, reduces the power dissipation.
After the oscillation of the main clock oscillation circuit has stabilized, the drive capacity of the XOUT pin
can be reduced using the XIN-XOUT drive capacity select bit (bit 5 at address 000716). Reducing the drive
capacity of the XOUT pin reduces the power dissipation. This bit defaults to "1" when shifting to stop mode
and after a reset. When shifting from low-speed/low power dissipation mode to stop mode, the value
before stop mode is retained.
You can switch over from the main clock to the ring oscillator by changing the value of the main clock
switch bit (bit 1 at address 000C16).
(2) Sub clock
The sub clock is generated by the sub clock oscillation circuit. No sub clock is generated after a reset.
After oscillation is started using the port Xc select bit (bit 4 at address 000616), the sub clock can be
selected as the BCLK by using the system clock select bit (bit 7 at address 000616). However, be sure
that the sub clock oscillation has fully stabilized before switching.
After the oscillation of the sub clock oscillation circuit has stabilized, the drive capacity of the XCOUT pin
can be reduced using the XCIN-XCOUT drive capacity select bit (bit 3 at address 000616). Reducing the
drive capacity of the XCOUT pin reduces the power dissipation. This bit changes to "1" when shifting to
stop mode and at a reset.
When the XCIN/XCOUT is used, set ports P86 and P87 as the input ports without pull-up.
(3) BCLK
The BCLK is the clock that drives the CPU and the watchdog timer, i.e. the internal clock , and is either
the main clock or fc or is derived by dividing the main clock by 2, 4, 8, or 16. After a reset the BCLK is
derived by dividing the main clock by 8 .
When shifting to stop mode, the main clock division select bit (bit 6 at address 000616) is set to "1".
When shifting from low-speed/low power dissipation mode to stop mode, the value before stop mode is
retainded.
(4) Peripheral function clocks
f2, f8, f32, f2SIO2, f8SIO2, f32SIO2
The clock for the peripheral devices is derived by dividing the main clock by 2 (or no division), 8, or 32.
The peripheral function clock is stopped by stopping the main clock or by setting the WAIT peripheral
function clock stop bit (bit 2 at address 000616) to "1" and then executing a WAIT instruction.
As to f2 and f2SIO2, you can select division by 2 or no division by changing the value of the peripheral
function clock select register.
f2AD
This clock is derived by dividing the main clock by 2 (or no division) and is used for A-D conversion. The
peripheral function clock is stopped by stopping the main clock or by setting the WAIT peripheral function
clock stop bit (bit 2 at address 000616) to "1" and then executing a WAIT instruction. You can select
division by 2 or no division by changing the value of the peripheral function clock select register.
Clock Generating Circuit