UPD78F0138 NEC, UPD78F0138 Datasheet - Page 137

• Manufacturer Part Number: UPD78F0138
• Description: (UPD78xxxx) 8-Bit Single-Chip Microcontrollers
• Manufacturer: NEC

5.6 Time Required to Switch Between Ring-OSC Clock and X1 Input Clock
clock.
are executed using the pre-switch clock after switching MCM0 (see Table 5-5).
stopping.
Bit 0 (MCM0) of the main clock mode register (MCM) is used to switch between the Ring-OSC clock and X1 input
In the actual switching operation, switching does not occur immediately after MCM0 rewrite; several instructions
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 original clock after switching the clock, wait for the number of clocks shown in Table 5-5 before
Caution To calculate the maximum time, set f
Remarks 1. PCC: Processor clock control register
Table 5-5. Time Required to Switch Between Ring-OSC Clock and X1 Input Clock
PCC2
0
0
0
0
1
2. f
3. f
4. The maximum time is the number of clocks of the CPU clock before switching.
PCC1
PCC
XP
R
: Ring-OSC clock oscillation frequency
0
0
1
1
0
: X1 input clock oscillation frequency
PCC0
0
1
0
1
0
CHAPTER 5 CLOCK GENERATOR
User’s Manual U16228EJ2V0UD
f
f
f
f
f
XP
XP
XP
XP
XP
/f
/2f
/4f
/8f
/16f
R
R
R
R
+ 1 clock
R
+ 1 clock
+ 1 clock
+ 1 clock
+ 1 clock
X1→Ring-OSC
Time Required for Switching
R
= 120 kHz.
2 clocks
Ring-OSC→X1
137