UPD78F9500MA-CAC-A Datasheet, PDF (84/342 Pages) Renesas Technology Corp – 8-Bit Single-Chip Microcontrollers

CHAPTER 5 CLOCK GENERATORS
5.5 Operation of CPU Clock Generator
A clock (fCPU) is supplied to the CPU from the system clock (fX) oscillated by one of the following three types of
oscillators.
• High-speed internal oscillator:
• Crystal/ceramic oscillator^{Note 1}:
• External clock input circuit:
Internally oscillates a clock of 8 MHz (TYP.).
Oscillates a clock of 2 MHz to 10 MHz.
Supplies a clock of 2 MHz to 10 MHz to X1 pin^{Note 2}.
<R> Notes 1. μPD78F920x only
<R>
2. μPD78F920x: X1 pin, μPD78F950x: EXCLK pin
The system clock oscillator is selected by the option byte. For details of the option byte, refer to CHAPTER 15
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
<R>
If the high-speed internal oscillator is selected as the oscillator, the X1 and X2 pins in μPD78F920x, and the
EXCLK pin in μPD78F950x 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
(a)
VDD
RESET _H
Internal reset
System clock
CPU clock
(b)
High-speed internal oscillation clock
PCC = 02H, PPCC = 02H
Option byte is read.
System clock is selected.
(Operation stops^Note)
Note Operation stop time is 277 μs (MIN.), 544 μs (TYP.), and 1.075 ms (MAX.).
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User’s Manual U18172EJ3V0UD