CHAPTER 5 CLOCK GENERATORS
User’s Manual U16898EJ3V0UD
75
5.5 Operation of CPU Clock Generator
A clock (f
CPU
) is supplied to the CPU from the system clock (f
X
) oscillated by one of the following three types of
oscillators.
•
High-speed internal oscillator:
Internally oscillates a clock of 8 MHz (TYP.).
•
Crystal/ceramic oscillator:
Oscillates a clock of 1 to 10 MHz.
•
External clock input circuit:
Supplies a clock of 1 to 10 MHz to X1 pin.
The system clock oscillator is selected by the option byte. For details of the option byte, refer to
CHAPTER 17
OPTION BYTE
.
(1) High-speed internal oscillator
When the high-speed internal oscillation is selected by the option byte, the following is possible.
•
Shortening of start time
If the high-speed internal oscillator is selected as the oscillator, the CPU can be started without having to wait
for the oscillation stabilization time of the system clock. Therefore, the start time can be shortened.
•
Improvement of expandability
If the high-speed internal oscillator is selected as the oscillator, the X1 and X2 pins can be used as I/O port
pins. For details, refer to
CHAPTER 4 PORT FUNCTIONS
.
Figures 5-8 and 5-9 show the timing chart and status transition diagram of the default start by the high-speed
internal oscillation.
Remark
When the high-speed internal oscillation is used, the clock accuracy is
±
5%.
Figure 5-8. Timing Chart of Default Start by High-Speed Internal Oscillation
V
DD
High-speed internal oscillation clock
PCC = 02H, PPCC = 02H
(a)
(b)
H
RESET
Internal reset
System clock
CPU clock
Option byte is read.
System clock is selected.
(Operation stops
Note
)
Note
Operation stop time is 277
µ
s (MIN.), 544
µ
s (TYP.), and 1.075 ms (MAX.).
