CHAPTER 5 CLOCK GENERATORS
User’s Manual U18172EJ2V0UD
72
Figure 5-7. Examples of Incorrect Resonator Connection (2/2)
(e) Signals are fetched
V
SS
X1
X2
5.4.3
External clock input circuit
This circuit supplies a clock from an external IC to the X1 pin.
If external clock input is selected by the option byte as the system clock source, the X2 pin can be used as an I/O
port pin.
For details of the option byte, refer to
CHAPTER 15 OPTION BYTE
. For details of I/O ports, refer to
CHAPTER 4
PORT FUNCTIONS
.
5.4.4 Prescaler
The prescaler divides the clock (f
X
) output by the system clock oscillator to generate a clock (f
XP
) to be supplied to
the peripheral hardware. It also divides the clock to peripheral hardware (f
XP
) to generate a clock to be supplied to the
CPU.
Remark
The clock output by the oscillator selected by the option byte (high-speed internal oscillator,
crystal/ceramic oscillator, or external clock input circuit) is divided. For details of the option byte, refer to
CHAPTER 15 OPTION BYTE
.