
S1C88409 TECHNICAL MANUAL
EPSON
59
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (Oscillation Circuit)
5.4.7 Programming notes
(1) The VD1 level must be switched while the
OSC3 oscillation circuit is off (before turning
on and after turning off). Switching during
operation may cause malfunction.
Furthermore, the VD1 voltage required at least
5 msec of voltage stabilizing time after switch-
ing. Do not turn the OSC3 oscillation circuit on
during this period.
(2) VD1 cannot be switched directly to a level that
is two or three levels different from the current
level. The middle level must be set between
switching.
To switch from 1,6 (3.2) V to 3.2 (1.6) V:
1.6 V
→ 2.4 V → 3.2 V
1.6 V
← 2.4 V ← 3.2 V
To switch from 1.6 (4.2) V to 4.2 (1.6) V:
1.6 V
→ 2.4 V → 3.2 V → 4.2 V
1.6 V
← 2.4 V ← 3.2 V ← 4.2 V
To switch from 2.4 (4.2) V to 4.2 (2.4) V:
2.4 V
→ 3.2 V → 4.2 V
2.4 V
← 3.2 V ← 4.2 V
A 5 msec interval is required for each switching
step.
(3) To generate VD1 with specified voltage, the
supply voltage must be higher than the
specified voltage.
To prevent malfunction, make sure that the
supply voltage is not lowered under the VD1
value to be set using the SVD circuit before
switching VD1. Do not switch VD1 to a voltage
higher than the supply voltage if the supply
voltage drops.
(4) The OSC3 oscillation circuit takes a maximum
20 msec for stabilizing oscillation after turning
the OSC3 oscillation circuit on. Therefore, take
an enough interval after the OSC3 oscillation
goes on before starting control of the periph-
eral circuit, such as the programmable timer,
serial interface and A/D converter, that uses
the OSC3 oscillation circuit as the clock source.
(The oscillation start time varies depending on
the oscillator and external component to be
used. Refer to Chapter 8, "ELECTRICAL
CHARACTERISTICS", in which an example of
oscillation start time is indicated.)
(5) Use a separate instruction for switching the
clock from OSC3 to OSC1 and turning the
OSC3 oscillation off. Handling with one
instruction may cause malfunction of the CPU.
(6) To prevent malfunction, before stopping the
OSC3 oscillation, stop the operation of the
peripheral circuits that use the OSC3 oscillation
circuit as the clock source, such as program-
mable timer, serial interface and A/D con-
verter.
(7) Do not turn the OSC3 oscillation circuit on to
reduce current consumption when the OSC3
clock is not necessary.