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CHAPTER 3 CPU
■
Instruction Cycle (t
INST
)
For instruction cycles (minimum instruction run time), a 1/4, 1/8, 1/16, or 1/64 frequency can be selected
using the clock speed selection bits (CS1 and CS0).
In active mode, when the oscillation frequency (F
CH
) is 12.5 MHz, the instruction cycle for the maximum
speed (SYCC: CS1 and CS0 = 11
B
) is 4/F
CH
(= about 0.32 µs).
Table 3.6-1 Explanation of Functions of Each Bit in the System Clock Control Register (SYCC)
Bit name Description
bit7
SCM: System clock
monitor bit
Used to check the current clock mode.
When this bit is 0, the clock is stopping or waiting for stabilization of oscillation.
When this bit is 1, operations are performed in active mode.
Note:
This bit is read-only enabled. Writing a value to this bit does not affect
operation.
bit6,
bit5
Unused bits
Values in these bits are undefined when read.
Writing values into these bits does not affect operation.
bit4,
bit3
WT1, WT0:
Oscillation
stabilization wait time
selection bits
Used to select an oscillation stabilization wait time setting.
When external interrupt causes a return from stop mode to active mode, the
oscillation stabilization wait time setting selected by these bits is applied.
The initial values of these bits are determined by options. Therefore, when an
oscillation stabilization wait time setting is to be applied for a reset, it is selected by
options.
Note:
Change values in these bits after confirming that the clock is not waiting for
stabilization of oscillation using the SCM bit.
bit2 Unused bit
This bit is always "1" when read.
Note:
Specify "1".
bit1,
bit0
CS1, CS0:
Clock speed selection
bits
Used to select the clock speed in active mode.
One of four operating clock speeds (gears) can be specified for the CPU and
peripheral functions. However, these bits do not affect the operating clock for the
time-base timer.