
S1C62440/624A0/624C0/62480 TECHNICAL HARDWARE
EPSON
I-45
CHAPTER 5: OSCILLATION CIRCUIT
Operating Voltage Change
S1C62440/4A0/4C0/480 can change OSC1 and OSC3
system clocks through the software. In this case, to obtain
stable operation, operating voltage VS1 of the internal circuit
is changed through the software.
Likewise, when selecting OSC1 as the system clock, there is
need to change operating voltage VS1 according to the value
of the power voltage (VDD–VSS).
Oscillation frequency and the corresponding operating
voltage VS1 are shown in Table 5.3.1.
5.3
Oscillation frequency
Oscillation circuit
Operating voltage VS1
32,768 Hz
OSC1
-1.2 V or -2.1 V
1 MHz
OSC3
-2.1 V
2 MHz
OSC3
-3.0 V
The VDD reference voltage is used as the operating voltage
VS1.
When OSC3 is to be used as the CPU system clock, change
the operating voltage VS1 accordingly through the software
and then turn the OSC3 oscillation ON and switch the clock
frequency.
If the OSC3 oscillation frequency is to be fixed around 1
MHz, set the operating voltage to -2.1 V; at 2 MHz, set the
operating voltage to -3.0 V.
Moreover, when the CPU is to be operated with OSC1, set
the operating voltage to -1.2 V if the power voltage detected
with the SVD circuit were less than 3.1 V (VDD–VSS < 3.1 V);
set the operating voltage to -2.1 V if the detected voltage
were 3.1 V or more (VDD–VSS
≥ 3.1 V). However, it can be
used fixed at -1.2 V (at OSC1 operation) for power whose
initial value is 3.6 V or less as in lithium batteries.
Switching VS1 when the power source voltage is lower than the set
voltage may cause misoperation. Perform the operating voltage
only after making sure that power voltage by SVD is more than the
VS1 setting voltage (absolute value).
Note
Table 5.3.1
Oscillation frequency and
operating voltage