CHAPTER 5 CLOCK GENERATORS
User’s Manual U18172EJ2V0UD
68
The fastest instruction of the 78K0S/KU1+ is executed in two CPU clocks. 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
CPU Clock (f
CPU
)
Note
High-speed internal oscillation clock
(at 8.0 MHz (TYP.))
Crystal/ceramic oscillation clock
or external clock input (at 10.0 MHz)
f
X
0.25
µ
s 0.2
µ
s
f
X
/2 0.5
µ
s 0.4
µ
s
f
X
/2
2
1.0
µ
s 0.8
µ
s
f
X
/2
3
2.0
µ
s 1.6
µ
s
f
X
/2
4
4.0
µ
s 3.2
µ
s
Note
The CPU clock (high-speed internal oscillation clock, crystal/ceramic oscillation clock, or external clock
input) is selected by the option byte.
(2) Low-speed internal oscillation mode register (LSRCM)
This register is used to select the operation mode of the low-speed internal oscillator (240 kHz (TYP.)).
This register is valid when it is specified by the option byte that the low-speed internal oscillator can be stopped
by software. If it is specified by the option byte that the low-speed internal oscillator cannot be stopped by
software, setting of this register is invalid, and the low-speed internal oscillator continues oscillating. In addition,
the source clock of WDT is fixed to the low-speed internal oscillator. For details, refer to
CHAPTER 8
WATCHDOG TIMER
.
LSRCM can be set by using a 1-bit or 8-bit memory manipulation instruction.
Reset signal generation sets LSRCM to 00H.
Figure 5-4. Format of Low-Speed internal oscillation Mode Register (LSRCM)
Address: FF58H, After reset: 00H, R/W
Symbol
7 6 5 4 3 2 1
<0>
LSRCM
0 0 0 0 0 0 0
LSRSTOP
LSRSTOP
Oscillation/stop of low-speed internal oscillator
0
Low-speed internal oscillates
1
Low-speed internal oscillator stops