CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U16315EJ1V0UD
116
(2) Improvement of performance
Because the CPU can be started without waiting for the X1 input clock oscillation stabilization time, the total
performance can be improved.
A timing diagram of the CPU default start using Ring-OSC is shown in Figure 5-12.
Figure 5-12. Timing Diagram of CPU Default Start Using Ring-OSC
Ring-OSC clock
(f
R
)
CPU clock
X1 input clock
(f
XP
)
Operation
stopped: 17/f
R
X1 oscillation stabilization time: 2
11
/f
XP
to 2
16
/f
XP
Note
RESET
Ring-OSC clock
X1 input clock
Switched by software
Subsystem clock
(f
XT
)
Note
Check using the oscillation stabilization time counter status register (OSTC).
(a) When the RESET signal is generated, bit 0 of the main clock mode register (MCM) is set to 0 and the Ring-
OSC clock is set as the CPU clock. However, a clock is supplied to the CPU after 17 clocks of the Ring-OSC
clock have elapsed after RESET release (or clock supply to the CPU stops for 17 clocks). During the
RESET period, oscillation of the X1 input clock and Ring-OSC clock is stopped.
(b) After RESET release, the CPU clock can be switched from the Ring-OSC clock to the X1 input clock using bit
0 (MCM0) of the main clock mode register (MCM) after the X1 input clock oscillation stabilization time has
elapsed. At this time, check the oscillation stabilization time using the oscillation stabilization time counter
status register (OSTC) before switching the CPU clock. The CPU clock status can be checked using bit 1
(MCS) of MCM.
(c) Ring-OSC can be set to stopped/oscillating using the Ring-OSC mode register (RCM) when “Can be stopped
by software” is selected for the Ring-OSC by a mask option, if the X1 input or subsystem clock is used as the
CPU clock. Make sure that MCS is 1 at this time.
(d) When Ring-OSC is used as the CPU clock, the X1 input clock can be set to stopped/oscillating using the
main OSC control register (MOC). Make sure that MCS is 0 at this time.
When the subsystem clock is used as the CPU clock, whether the X1 input clock stops or oscillates can be
set by the processor clock control register (PCC). In addition, HALT mode can be used during operation with
the subsystem clock, but STOP mode cannot be used (subsystem clock oscillation cannot be stopped by the
STOP instruction).