HD64336900G Datasheet, PDF (101/408 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Tiny Series

LSI operates on internal RC clock
Start (reset)
Write 1 to PMRC0 in CKCSR _[1]
Write 1 to PMRC1 in CKCSR
Write 0 to CKSWIE in CKCSR
Write 1 to OSCSEL in CKCSR [2]
[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[2:0] 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 internal RC clock.
Read the value of the CKSTA bit in CKCSR to
ensure that the system clocks are switched.
[3]
Switched to
No
external clock? (CKSTA in
CKCSR is 1)
Yes
LSI operates on external oscillator
Figure 5.4 Flowchart of Clock Switching with Backup Function Disabled (1)
(From Internal RC Clock to External Clock)
Rev. 1.00, 11/03, page 73 of 376