UPD78F0838 Renesas Electronics Corporation., UPD78F0838 Datasheet - Page 214

• Manufacturer Part Number: UPD78F0838
• Description: 8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

the internal high-speed oscillation clock and the high-speed system clock).
pre-switchover clock for several clocks (see Table 5-7).
ascertained using bit 1 (MCS) of MCM.
5.6.9 Conditions before clock oscillation is stopped
conditions before the clock oscillation is stopped.
212
Internal high-speed
oscillation clock
X1 clock
External main system clock
XT1 clock
External subsystem clock
By setting bit 0 (MCM0) of the main clock mode register (MCM), the main system clock can be switched (between
The actual switchover operation is not performed immediately after rewriting to MCM0; operation continues on the
Whether the CPU is operating on the internal high-speed oscillation clock or the high-speed system clock can be
Caution When switching the internal high-speed oscillation clock to the high-speed system clock, bit 2
Remarks 1. The number of clocks listed in Table 5-7 is the number of main system clocks before switchover.
The following lists the register flag settings for stopping the clock oscillation (disabling external clock input) and
Clock
2. Calculate the number of clocks in Table 5-7 by removing the decimal portion.
(XSEL) of MCM must be set to 1 in advance. The value of XSEL can be changed only once after a
reset release.
Set Value Before Switchover
Table 5-8. Conditions Before the Clock Oscillation is Stopped and Flag Settings
Example When switching the main system clock from the internal high-speed oscillation clock to the
Table 5-7. Maximum Time Required for Main System Clock Switchover
MCM0
0
1
high-speed system clock (@ oscillation with f
MCS = 1 or CLS = 1
(The CPU is operating on a clock other than the internal high-speed
oscillation clock)
MCS = 0 or CLS = 1
(The CPU is operating on a clock other than the high-speed system clock)
CLS = 0
(The CPU is operating on a clock other than the subsystem clock)
1 + 2f
OSC8
/f
Conditions Before Clock Oscillation is Stopped
IN
Preliminary User’s Manual U19748EJ1V0UD
CHAPTER 5 CLOCK GENERATOR
= 1 + 2
(External Clock Input Disabled)
8/10 = 1 + 2
1 + 2f
0
IN
Set Value After Switchover [clocks]
/f
OSC8
0.8 = 1 + 1.6 = 2.6
MCM0
OSC8
= 8 MHz, f
1 + 2f
IN
= 10 MHz)
1
OSC8
2 clocks
/f
IN
RSTOP = 1
MSTOP = 1
OSCSELS = 0
Flag Settings of SFR
Register