CHAPTER 6 PERIPHERAL HARDWARE FUNCTION
113
User’s Manual U10676EJ3V0UM
Figure 6-19. CPU Clock Switching Example
<1> Wait timeNote 1 to secure the oscillation stabilization time in response to RESET signal generation.
<2> The CPU starts operating at the lowest system clock speedNote 2.
<3> The PCC is rewritten and the device operates at maximum speed after the elapse of sufficient time
for the VDD pin voltage to increase to a level which allows maximum speed operation.
<4> Interruption of the commercial power is detected by means of interrupt input, etc., and the STOP mode
is entered.
<5> Wait timeNote 3 to secure the oscillation stabilization time after restoration of commercial power is
detected by means of an interrupt, etc., and the device is released from the STOP mode.
<6> Operates normally.
Notes 1.
µ
PD754144: Fixed to 56/fCC (56
µ
s at 1.0 MHz).
µ
PD754244: The wait time can be selected by a mask option.
Can be selected from 215/fX = 7.81 ms or 217/fX = 31.3 ms at 4.19 MHz,
and from 215/fX = 5.46 ms or 217/fX = 21.8 ms at 6.0 MHz.
2.
µ
PD754144: 64
µ
s at fCC = 1.0 MHz.
µ
PD754244: 15.3
µ
s at 4.19 MHz and 10.7
µ
s at 6.0 MHz
3.
µ
PD754144: 29/fCC (512
µ
s at 1.0 MHz)
µ
PD754244: The following four times can be selected by BTM:
220/fX, 217/fX, 215/fX, 213/fX
On
Off
Commercial power supply
V
DD
pin voltage
RESET signal
CPU clock
<1> Wait
Note 1
<5> Wait
Note 3
<2> Lowest speed
of system clock
Note 2
<3> 0.67 s <4> STOP mode <6> 0.67 s
Internal reset operation
f
X
f
X
f
X
µµ
Minimum operating
supply voltage