
S1C62440/624A0/624C0/62480 TECHNICAL SOFTWARE
EPSON
II-109
CHAPTER 7: SUMMARY OF NOTES
(1) When high-speed operation of the CPU is not required,
observe the following reminders to minimize power cur-
rent consumption.
Set the CPU operating clock to OSC1.
Turn the OSC3 oscillation OFF.
Set the internal operating voltage (VS1) to -1.2 V or -2.1 V.
(2) Before you use OSC1 as system clock, you should check
the supply voltage (VSS) using the SVD circuit.
If the SVD circuit detects supply voltage less than 3.1 V
(VDD–VSS < 3.1 V) then set the operating voltage (VS1) to
-1.2 V. Or if the SVD circuit detects supply voltage 3.1 V
or more (VDD–VSS
≥ 3.1 V) then set VS1 to -2.1 V.
Moreover, because -1.2 V will be set during initial reset,
be sure to execute the previous process at the beginning
of the initial routine.
(3) When switching VS1 from -1.2 V (for OSC1 crystal oscilla-
tion circuit) to -3.0 V (for OSC3 oscillation circuit), or vice
versa, be sure to hold the -2.1 V setting for more than 5
ms first for power voltage stabilization.
(VSC1, VSC0) = (0, 0)
→ (0, 1) → 5 ms WAIT → (1, ×)
= (1,
×) → (0, 1) → 5 ms WAIT → (0, 0)
= (0, 0)
→ (1, ×) is prohibited
= (1,
×) → (0, 0) is prohibited
Furthermore, perform the switch after making sure that
power voltage by SVD is more than the VS1 (absolute
value) set voltage. Switching VS1 when the power source
voltage is lower than the set voltage may cause malfunc-
tion.
(4) When switching the CPU operating clock from OSC1 to
OSC3, follow the flow chart shown in Figure 6.2.2 and
then proceed with software processing.
(5) Use separate instructions to switch the clock from OSC3
to OSC1 and turn the OSC3 oscillation OFF. Simultane-
ous processing with a single instruction may cause
malfunction of the CPU.
(6) In the S1C62440/4C0/480, when CR oscillation has
been selected by the mask option, internal regulated
voltage becomes -2.1 V and will never become -1.2 V.
Oscillation circuit