65
3.7 Clock
*: Options can be selected only for MB89577.
Table 3.7-1 Explanation of the Functions of Each Bit of the System Clock Control Register (SYCC)
Bit name
Function
Bit 7
SCM:
System clock monitor bit
Bit to check the current clock mode (operating clock)
If the bit is "0", the system is operating in subclock mode
(The main clock is stopped or waiting for oscillation
stabilization to make a transition to the main clock mode).
If the bit is "1", the system is operating in main clock
mode.
[Reference:]
This bit is read-only. Write operation to this bit has no
significance and does not affect operations.
Bit 6
Bit 5
Unused bits
The read value is undefined.
Writing has no effect on operation.
Bit 4
Bit 3
WT1, WT0:
Oscillation stabilization wait
time select bits
Bits to select the oscillation stabilization wait time of the
main clock
The oscillation stabilization wait time selected by these
bits is taken when making a transition from the subclock
mode to the main clock mode, or returning to normal
operation from the main stop mode by an external
interrupt.
The initial values of these bits are selected by option
settings *. Thus, if an oscillation stabilization wait time is
taken for a reset, the oscillation stabilization wait time
selected by option settings is taken.
Note:
Do not rewrite these bits simultaneously when switching
from the subclock to the main clock (SCS=1 --> 0).
Before rewriting the bits, check that the oscillation
stabilization is not waited upon using the SCM bit.
Bit 2
SCS:
System clock select bit
Bit to specify the clock mode
A transition from the main clock mode to the subclock
mode is caused by writing "0" into this bit.
If "1" is written into this bit, the transition from the
subclock mode to the main clock mode occurs after taking
the oscillation stabilization wait time set by the WT1 and
WT0 bits.
Note:
If the single clock system option is selected, this bit has
no significance. Set always "1".
Bit 1
Bit 0
CS1, CS0:
Main clock speed select bits
Bit to select the clock speed in main clock mode.
Four different speeds of the operating clock can be
selected for CPU and each peripheral function (gear
function). However, the operating clock of the timebase
timer and watch prescaler is not affected by these bits.