24
Status Transition of BCLK
M
i
t
s
u
M
S
b
i
s
3
M
h
0
I
C
i
m
2
R
i
1
O
c
r
8
C
o
c
o
G
M
m
p
r
P
u
t
u
T
e
r
p
R
s
o
U
S
I
N
G
L
E
-
C
H
I
P
1
6
-
B
I
T
C
M
O
O
E
CM17
0
1
Invalid
1
0
Invalid
Invalid
CM16
1
0
Invalid
1
0
Invalid
Invalid
CM07
0
0
0
0
0
1
1
CM06
0
0
1
0
0
Invalid
Invalid
CM05
0
0
0
0
0
0
1
CM04
Invalid
Invalid
Invalid
Invalid
Invalid
1
1
Operating mode of BCLK
Division by 2 mode
Division by 4 mode
Division by 8 mode
Division by 16 mode
No-division mode
Low-speed mode
Low power dissipation mode
Table 5. Operating modes dictated by settings of system clock control registers 0 and 1
Status Transition Of BCLK
Power dissipation can be reduced and low-voltage operation achieved by changing the count source for
BCLK. Table WA-4 shows the operating modes corresponding to the settings of system clock control
registers 0 and 1.
When reset, the device starts in division by 8 mode. The main clock division select bit 0(bit 6 at address
0006
16
) changes to “1” when shifting from high-speed/medium-speed 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.
The following shows the operational modes of BCLK.
(1) Division by 2 mode
The main clock is divided by 2 to obtain the BCLK.
(2) Division by 4 mode
The main clock is divided by 4 to obtain the BCLK.
(3) Division by 8 mode
The main clock is divided by 8 to obtain the BCLK. When reset, the device starts operating from this
mode, the main clock must be oscillating stably. When going to low-speed or lower power consumption
mode, make sure the sub-clock is oscillating stably.
(4) Division by 16 mode
The main clock is divided by 16 to obtain the BCLK.
(5) No-division mode
The main clock is divided by 1 to obtain the BCLK.
(6) Low-speed mode
f
C
is used as the BCLK. Note that oscillation of both the main and sub-clocks must have stabilized before
transferring from this mode to another or vice versa. At least 2 to 3 seconds are required after the sub-
clock starts. Therefore, the program must be written to wait until this clock has stabilized immediately
after powering up and after stop mode is cancelled.
(7) Low power dissipation mode
f
C
is the BCLK and the main clock is stopped.
Note : Before the count source for BCLK can be changed from X
IN
to X
CIN
or vice versa, the clock to which
the count source is going to be switched must be oscillating stably. Allow a wait time in software for
the oscillation to stabilize before switching over the clock.