HD64F3687GHV Datasheet, PDF (114/566 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 5 Clock Pulse Generator
LSI operates on on-chip oscillator clock
[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.
Start (reset)
[2] The external oscillator halt detecting circuit is
enabled when the external oscillation backup
function is enabled. Since this detecting circuit
operates on the on-chip oscillator clock, do not set
Write 1 to PMRC0 in CKCSR _[1]
Write 1 to PMRC1 in CKCSR
the on-chip oscillator to standby mode by using the
RCSTP bit in RCCR.
[3] An interrupt to switch from the on-chip oscillator
clock to the external oscillator is enabled.
[4] After writing 1 to the OSCSEL bit, this LSI waits
until the oscillation of the external oscillator settles.
Write 1 to OSCBAKE in CKCSR [2]
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
Clear CKSWIF in CKCSR to 0
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).
Write 1 to CKSWIE in CKCSR ^[3]
[5] While waiting for external oscillation settling, this
LSI is not halted but continues to operate on the on-
chip oscillator clock. Read the CKSTA bit in CKCSR
to ensure whether or not clocks are switched. When
Write 1 to OSCSEL in CKCSR ^[4]
the oscillation settles, this LSI switches the system
clocks to the external clock. If the external oscillator
is halted, then set the clock switching interrupt
request flag.
[6] If this LSI detects the external oscillator halt, it
Switched to
external clock? (CKSTA in
CKCSR is 1)
Yes
[5]
No
switches the system clocks to the on-chip oscillator
clock, and sets the clock switching interrupt request
flag.
External
oscillator halt
is detected*
LSI operates on
on-chip oscillator clock
[6]
LSI operates on external clock
External oscillator
halt is detected*
Exception handling
for clock switching
Note: * To prevent the LSI from malfunctioning at the external oscillation halt, switching the clock source along
with the watchdog timer is highly recommended.
Figure 5.3 Flowchart of Clock Switching with Backup Function Enabled
Rev. 3.00 Sep. 10, 2007 Page 80 of 528
REJ09B0216-0300