HD64F3687GHV Datasheet, PDF (115/566 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 5 Clock Pulse Generator
LSI operates on on-chip oscillator clock
Start (reset)
Write 1 to PMRC0 in CKCSR _[1]
Write 1 to PMRC1 in CKCSR
Write 0 to CKSWIF in CKCSR
Write 1 to OSCSEL in CKCSR [2]
[3]
Switched to
No
external clock? (CKSTA in
CKCSR is 1)
Yes
[1] External oscillation starts to be enabled when
pins PC1 and PC0 are specified as external
clock 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 on-chip oscillator
clock. Read the value of the CKSTA bit in
CKCSR to ensure that the system clocks are
switched.
LSI operates on external oscillator
Figure 5.4 Flowchart of Clock Switching with Backup Function Disabled (1)
(From On-Chip Oscillator Clock to External Clock)
Rev. 3.00 Sep. 10, 2007 Page 81 of 528
REJ09B0216-0300