Datasheet

Section 5 Clock Pulse Generators
Rev. 3.00 Sep. 14, 2006 Page 76 of 408
REJ09B0105-0300
5.3.1 Clock Control Operation
The LSI system clock is generated by the on-chip oscillator clock after a reset. The on-chip
oscillator clock is switched to the external clock by the user software.
Yes
No
[1]
[1] External oscillation starts when pins PC1 and PC0
are selected as external oscillation pins. Write 0 to
bit PMRC1 to input the external clock.
[2] After writing 1 to the OSCSEL bit, this LSI waits
until the oscillation of the external oscillator
settles. The correspondence between Nwait,
which is the number of wait cycles for oscillation
settling, and Nstby, which is the number of wait
cycles for oscillation settling when returning from
standby mode, is as follows:
Nstby ≤ Nwait ≤ 2 × Nstby
Nstby is set by bits STS 2 to 0 in SYSCR1.
For details, see section 6.1.1, System Control
Register 1 (SYSCR1).
[3] While the system is waiting for the external
oscillation settling, this LSI is not halted but
continues to operate on the on-chip oscillator clock.
Read the value of the CKSTA bit in CKCSR to
ensure that the system clocks are switched.
LSI operates on on-chip oscillator RC clock
Start (reset)
Write 1 to PMRC0 in CKCSR
Write 1 to PMRC1 in CKCSR
Write 0 to CKSWIE in CKCSR
Write 1 to OSCSEL in CKCSR
Switched to
external clock? (CKSTA in
CKCSR is 1)
LSI operates on external oscillator
[2]
[3]
Figure 5.3 Flowchart of Clock Switching On-chip Oscillator
Clock to External Clock (1)