CHAPTER 5 CLOCK GENERATORS
Preliminary User’s Manual U16898EJ1V0UD
66
The fastest instruction of the 78K0S/KA1+ 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 Ring-OSC 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 Ring-OSC clock, crystal/ceramic oscillation clock, or external clock input) is
selected by the option byte.
(2) Low-speed Ring-OSC mode register (LSRCM)
This register is used to select the operation mode of the low-speed Ring-OSC oscillator (240 kHz (TYP.)).
This register is valid when it is specified by the option byte that the low-speed Ring-OSC oscillator can be
stopped by software. If it is specified by the option byte that the low-speed Ring-OSC oscillator cannot be
stopped by software, setting of this register is invalid, and the low-speed Ring-OSC oscillator continues
oscillating. In addition, the source clock of WDT is fixed to the low-speed Ring-OSC oscillator. For details, refer
to CHAPTER 9 WATCHDOG TIMER.
LSRCM can be set by using an 8-bit memory manipulation instruction.
Reset input sets LSRCM to 00H.
Figure 5-4. Format of Low-Speed Ring-OSC 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 Ring-OSC
0
Low-speed Ring-OSC oscillates
1
Low-speed Ring-OSC stops
(3) High-speed Ring-OSC mode register (HSRCM)
This register is used to select the operation mode of the high-speed Ring-OSC oscillator that generates a clock (8
MHz (TYP.)) for controlling self programming of the flash memory.
This register is valid when crystal/ceramic oscillation or external clock input is selected as the system clock
source by the option byte. Setting of this register is invalid when the high-speed Ring-OSC oscillator is selected
by the option byte.
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