CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U16315EJ1V0UD
122
5.6 Time Required to Switch Between Ring-OSC Clock and X1 Input Clock
Bit 0 (MCM0) of the main clock mode register (MCM) is used to switch between the Ring-OSC clock and X1 input
clock.
In the actual switching operation, switching does not occur immediately after MCM0 rewrite; several instructions
are executed using the pre-switch clock after switching MCM0 (see
Table 5-5
).
Bit 1 (MCS) of MCM is used to judge that operation is performed using either the Ring-OSC clock or X1 input clock.
To stop the clock, wait for the number of clocks shown in Table 5-5 before stopping.
Table 5-5. Time Required to Switch Between Ring-OSC Clock and X1 Input Clock
PCC
Time Required for Switching
PCC2
PCC1
PCC0
X1
→
Ring-OSC
Ring-OSC
→
X1
0
0
0
f
XP
/f
R
+ 1 clock
0
0
1
f
XP
/2f
R
+ 1 clock
0
1
0
f
XP
/4f
R
+ 1 clock
0
1
1
f
XP
/8f
R
+ 1 clock
1
0
0
f
XP
/16f
R
+ 1 clock
2 clocks
Caution
To calculate the maximum time, set f
R
= 120 kHz.
Remarks 1.
PCC: Processor clock control register
2.
f
XP
: X1 input clock oscillation frequency
3.
f
R
: Ring-OSC clock oscillation frequency
4.
The maximum time is the number of clocks of the CPU clock before switching.