UPD78F0138 NEC, UPD78F0138 Datasheet - Page 138

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

5.7 Time Required for CPU Clock Switchover
register (PCC).
the pre-switchover clock for several instructions (see Table 5-6).
ascertained using bit 5 (CLS) of the PCC register.
138
CSS PCC2 PCC1 PCC0
Set Value Before
0
1
The CPU clock can be switched using bits 0 to 2 (PCC0 to PCC2) and bit 4 (CSS) of the processor clock control
The actual switchover operation is not performed immediately after rewriting to the PCC; operation continues on
Whether the system is operating on the X1 input clock (or Ring-OSC clock) or the subsystem clock can be
Remarks 1. The maximum time is the number of clocks of the pre-switchover CPU clock.
Caution Selection of the CPU clock cycle division factor (PCC0 to PCC2) and switchover from the X1
Switchover
0
0
0
0
1
×
0
0
1
1
0
×
2. Figures in parentheses apply to operation with f
input clock to the subsystem clock (changing CSS from 0 to 1) should not be set
simultaneously.
Simultaneous setting is possible, however, for selection of the CPU clock cycle division factor
(PCC0 to PCC2) and switchover from the subsystem clock to the X1 input clock (changing CSS
from 1 to 0).
0
1
0
1
0
×
CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0
0
8 clocks
4 clocks
2 clocks
1 clock
1 clock
0
Table 5-6. Maximum Time Required for CPU Clock Switchover
0
0
0
16 clocks
4 clocks
2 clocks
1 clock
1 clock
0
CHAPTER 5 CLOCK GENERATOR
0
User’s Manual U16228EJ2V0UD
1
0
16 clocks
8 clocks
2 clocks
Set Value After Switchover
1 clock
1 clock
0
1
XP
0
= 10 MHz and f
0
16 clocks
8 clocks
4 clocks
1 clock
1 clock
0
1
1
XT
= 32.768 kHz.
0
16 clocks
8 clocks
4 clocks
2 clocks
1 clock
1
0
0
1
f
f
f
f
XP
f
XP
XP
XP
(306 clocks)
(153 clocks)
XP
(77 clocks)
(39 clocks)
(20 clocks)
/16f
/2f
/4f
/8f
/f
×
XT
XT
XT
XT
XT
clocks
clocks
clocks
clocks
clocks
×
×