Datasheet

Section 5 Clock Pulse Generator
Rev. 2.00 Jul. 04, 2007 Page 90 of 692
REJ09B0309-0200
5.2.4 Selecting On-Chip Oscillator for System Clock
The on-chip oscillator is selected by the input level on the IRQAEC pin during a reset*. The
selection of the system clock oscillator or on-chip oscillator for the system clock is as listed in
table 5.1. The level being input on the IRQAEC pin during a reset should be fixed to either Vcc or
GND, depending on the oscillator type to be selected. The level will be determined upon reset
cancellation
When the on-chip oscillator for the system clock is selected, connection of a resonator to OSC1 or
OSC2 is not necessary. In this case, the OSC1 pin should be fixed to Vcc or GND. The OSC2 pin
should be left open.
Notes: When programming or erasing the flash memory, e.g. by on-board programming, the
system clock oscillator should always be selected. Use of the on-chip emulator requires
either a connected resonator or the supply of an external clock signal, even if the on-chip
oscillator for the system clock is selected.
* This reset represents an external reset or power-on reset, but not a reset by the
watchdog timer.
Table 5.1 Selection of the System Clock Oscillator or On-Chip Oscillator for the System
Clock
IRQAEC Input Level
(During a Reset)
Oscillator of System Clock Pulse
Generator Circuit
OSCF IRQAECF
Low System clock oscillator 0 0
High On-chip oscillator for system clock 1 1