H838024 datasheet(152/697 Pages) RENESAS

152 / 697 page

Section 4 Clock Pulse Generators

Rev. 7.00 Mar 10, 2005 page 110 of 652

REJ09B0042-0700

External Clock Input Method

Connect an external clock signal to pin OSC1, and leave pin OSC2 open. Figure 4.7 shows a

typical connection.

OSC1

OSC2

External clock input

Open

Figure 4.7 External Clock Input (Example)

Frequency

Oscillator Clock (

φφφφOSC)

Duty cycle

45% to 55%

On-Chip Oscillator Selection Method (H8/38124 Group Only)

The on-chip oscillator is selected by setting the IRQAEC pin input level during resets.* Table 4.3

lists the methods for selecting the system clock oscillator and the on-chip oscillator. The IRQAEC

pin input level set during resets must be fixed at VCC or GND, based on the oscillator to be

selected. It is not necessary to connect an oscillator to pins OSC1 and OSC2 if the on-chip

oscillator is selected. In this case, pin OSC1 should be fixed at VCC or GND.

Note:

The system clock oscillator must be selected in order to program or erase flash memory as

part of operations such as on-board programming. Also, when using the on-chip emulator,

an oscillator should be connected, or an external clock input, even if the on-chip oscillator

is selected.

Other than watchdog timer or low-voltage detect circuit reset.

Table 4.3

System Clock Oscillator and On-Chip Oscillator Selection Methods

IRQAEC pin input level (during resets)

System clock oscillator

Enabled

Disabled

On-chip oscillator

Disabled

Enabled

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