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CHAPTER 3 CPU
I Instruction cycle (tinst)
Instruction cycle (minimum execution time) can be selected as
1/4, 1/8, 1/16, or 1/64 of the main clock. The selection is made by main clock speed select bits (CS1 and
CS0) of the SYCC register.
With main clock mode, and the highest clock speed selected (SYCC: SCS = 1, CS1 = 1, CS0 = 1), and with
a main clock source oscillation (FCH) of 12.5 MHz, the instruction cycle is 4/FCH = approximately 0.32 s.
With subclock mode selected (SCS = 0), and with a subclock source oscillation (FCL) of 32.768 kHz, the
instruction cycle is 2/FCL= approximately 61.0 s.
Table 3.6-1 System clock control register (SYCC) bits
Bit
Function
Bit 7
SCM:
System clock monitor
bit
Indicates the current clock mode (operating clock).
"0" indicates subclock mode (main clock is stopped or in the oscillation stabilization
wait time to go to main clock mode).
"1" indicates main clock mode.
Note:
This is a read-only bit. Writing to it has no effect.
Bit 6
Unused bits
The read value is indeterminate.
Writing to these bits has no effect on operation.
Bit5
Reserved bit
This bit must always set to 1
Bit 4
Bit 3
WT1, WT0:
Oscillation
stabilization wait time
select bits
Select main clock oscillation stabilization wait time.
Selected wait time applies if external interrupt causes "wakeup" from main-stop
mode (transition to normal (run) mode).
Initial value of these bits is an option selection. Accordingly, when an oscillation
stabilization wait time is provided at reset, the wait time will be as selected by the
option.
Note:
These bits should not be changed at the same time switching from subclock to main
clock (SCS = 1 --> 0). Before changing the bits, first check the SCM bit to verify
that the device is not currently in the stabilization wait time.
Bit 2
SCS:
System clock
select bit
Specifies the clock mode.
Writing "0" to this bit sets the CPU changing from main clock to subclock mode.
Writing "1" to this bit causes the device to go from subclock to main clock mode
after the oscillation stabilization wait time set by WT1 and WT0 bits.
Note:
If the single clock option is selected, this bit has no function. It should be set to "1".
Bit 1
Bit 0
CS1, CS0:
Main clock speed
select bits
These bits select the clock speed for the main clock mode.
Four different speeds can be set for CPU and peripheral function operating clocks
(speed-shift function). The clock that clock the timebase timer is not affected by
these bits.