Time Required To Switch Between Ring-Osc Clock And X1 Input Clock - NEC 78K0 User Manual

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 original clock after switching the clock, wait for the number of clocks shown in Table 5-5.
Table 5-5. Maximum Time Required to Switch Between Ring-OSC Clock and X1 Input Clock
PCC2
0
0
0
0
1
Caution To calculate the maximum time, set f
Remarks 1. PCC: Processor clock control register
2. f
3. f
4. The maximum time is the number of clocks of the CPU clock before switching.
CHAPTER 5 CLOCK GENERATOR
PCC
PCC1 PCC0
0 0 f /f + 1 clock
XP R
0 1 f /2f + 1 clock
XP R
1 0 f /4f + 1 clock
XP R
1 1 f /8f + 1 clock
XP R
0 0 f /16f + 1 clock
XP R
: X1 input clock oscillation frequency
XP
: Ring-OSC clock oscillation frequency
R
User's Manual U16227EJ2V0UD
Maximum Time Required for Switching
X1→Ring-OSC
= 120 kHz.
R
Ring-OSC→X1
2 clocks
117