CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U19014EJ1V0UD
86
(2) Processor clock control register (PCC)
This register is used to select the CPU clock and the division ratio.
PCC is set by a 1-bit or 8-bit memory manipulation instruction.
Reset signal generation sets PCC to 01H.
Figure 5-3. Format of Processor Clock Control Register (PCC)
Address: FFFBH After reset: 01H R/W
Symbol
7 6 5 4 3 2 1 0
PCC 0 0 0 0 0
PCC2
PCC1
PCC0
Caution
Be sure to clear bits 3 and 7 to 0.
Remark
f
XP
: Main system clock oscillation frequency
The fastest instruction can be executed in 2 clocks of the CPU clock in the
µ
PD78F0730. Therefore, the
relationship between the CPU clock (f
CPU
) and the minimum instruction execution time is as shown in Table 5-2.
Table 5-2. Relationship Between CPU Clock and Minimum Instruction Execution Time
Minimum Instruction Execution Time: 2/f
CPU
High-Speed System Clock
Note
Internal High-Speed Oscillation Clock
Note
CPU Clock (f
CPU
)
At 12 MHz Operation
At 16 MHz Operation
At 16 MHz (TYP.) Operation
f
XP
0.167
µ
s 0.125
µ
s 0.125
µ
s (TYP.)
f
XP
/2 0.333
µ
s 0.25
µ
s 0.25
µ
s (TYP.)
f
XP
/2
2
0.667
µ
s 0.5
µ
s 0.5
µ
s (TYP.)
f
XP
/2
3
1.33
µ
s 1.0
µ
s 1.0
µ
s (TYP.)
f
XP
/2
4
2.67
µ
s 2.0
µ
s 2.0
µ
s (TYP.)
Note
The main clock mode register (MCM) is used to set the main system clock supplied to CPU clock (high-
speed system clock/internal high-speed oscillation clock) (see
Figure 5-6
).
PCC2
PCC1
PCC0
CPU
clock
(f
CPU
) selection
0 0 0
f
XP
0 0 1
f
XP
/2 (default)
0 1 0
f
XP
/2
2
0 1 1
f
XP
/2
3
1 0 0
f
XP
/2
4
Other than above
Setting prohibited
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