
60
EPSON
S1C88409 TECHNICAL MANUAL
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (Prescaler and Clock Control Circuit)
5.5 Prescaler and Clock Control
Circuit for Peripheral Circuits
5.5.1 Configuration of prescaler
The S1C88409 has a prescaler that generates the
clocks for the internal peripheral circuit by divid-
ing the output clock of the OSC1 oscillation circuit
and OSC3 oscillation circuit.
The division ratio of the prescaler can be selected
individually for each peripheral circuit by soft-
ware.
Furthermore, the clock control circuit is provided
to control clock supply to each peripheral circuit.
The peripheral circuits which use the output clock
are as follows:
16-bit programmable timer 0
16-bit programmable timer 1
8-bit programmable timer
Clock output (FOUT1, FOUT3)
A/D converter
Touch panel controller
Figure 5.5.1.1 shows the configuration of the
prescaler.
For control of each peripheral circuit, refer to
respective section.
Selector &
ON/OFF control
1/1
1/2
1/4
1/8
1/128
fOSC1
FOUT1
Selector &
ON/OFF control
Selector &
ON/OFF control
Selector &
ON/OFF control
FOUT3
Selector &
ON/OFF control
Touch panel controller
Selector &
ON/OFF control
A/D converter
Selector &
ON/OFF control
8-bit
programmable timer
Selector &
ON/OFF control
16-bit
programmable timer 1
Selector &
ON/OFF control
16-bit
programmable timer 0
EXCL01 (K11)
EXCL00 (K10)
1/1
1/2
1/4
1/8
1/4096
fOSC3
Fig. 5.5.1.1 Configuration of prescaler and clock
control circuit
5.5.2 Setting of source clock
The prescaler uses the OSC1 clock and OSC3 clock
as the source clocks.
The OSC1 prescaler always operates except for
SLEEP status. When using an output clock from
the OSC3 prescaler, it is necessary to turn the
OSC3 oscillation circuit on.
Refer to Section 5.4.5, "Switching of CPU clock and
operating voltage VD1" for control of the OSC3
oscillation circuit and switching of the CPU
operating clock.
At initial reset, the OSC3 oscillation circuit stops.
The OSC3 oscillation circuit takes a maximum 20
msec for stabilizing oscillation after turning the
OSC3 oscillation circuit on. Therefore, wait a long
enough interval after the OSC3 oscillation goes on
before turning the clock output of the OSC3
prescaler on. (The oscillation start time varies
depending on the oscillator and external compo-
nents to be used. Refer to Chapter 8, "ELECTRI-
CAL CHARACTERISTICS", in which an example
of oscillation start time is indicated.)
Among the peripheral circuits that use the clock
output from the prescaler, the 16-bit program-
mable timer can select the clock source from either
OSC1 or OSC3. Select the clock source before
supplying the clock to the 16-bit programmable
timer.