
S1C88409 TECHNICAL MANUAL
EPSON
159
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (Touch Panel Controller)
Connecting a touch panel
A touch panel consists of two panels for X coordi-
nate detection and Y coordinate detection that are
equipped with two electrodes each. The BXH, BXL,
BYH and BYL signals should be connected as
shown in Figure 5.17.2.1 to control the electrodes
individually. Further the negative electrodes
should be connected to the analog input terminals
selected by mask option to input the detection
results. The capacitors to connect to Ch0 and Ch1
should be 1000 pF or less.
BXH
BXL
BYH
BYL
Ch0
Ch1
X panel
Y panel
These capasitor should
be 1000 pF or less.
Fig. 5.17.2.1 Connecting touch panel
5.17.3 Operation of touch panel controller
Control of A/D converter
Since the touch panel controller controls A/D
conversion for coordinate values, it is unnecessary
to control with software. However, the clock to be
supplied to the A/D converter must be controlled
by software. Furthermore, since the A/D converter
interrupt can occur even when used for the touch
panel, mask the interrupt by software.
Refer to Section 5.18, "A/D Converter", for details
of the A/D converter.
Pen-down check
Coordinate detection increases current consump-
tion because it always operates in high speed.
Therefore, coordinate detection should be stopped
to suppress current consumption when the touch
panel operation is not necessary. To detect a start
of touch panel operation (pen down), the pen-
down check mode is provided.
The pen-down check mode controls the signals as
follows:
BXH=HIGH (The positive electrode on the X
panel goes off.)
BXL=LOW
(The negative electrode on the X
panel goes on.)
BYH=Pen-down check pulse
(The positive electrode on the Y
panel goes off.)
BYL=HIGH (The negative electrode on the Y
panel goes off.)
In the pen-down check mode, the pen-down
detection input is pulled up in the touch panel
controller and it goes high in pen-up status.
In pen-down status, the output becomes low level
due to the pressurization on the X panel.
The pen-down check starts by writing "1" to the
PDC register and stops by writing "0".
When the touch panel controller judges pen-down
status due to a low level input, a pen-down
interrupt occurs.
The pen-down check by the PDC register uses the
OSC1 clock and does not need the OSC3 clock.
This makes it possible to reduce current consump-
tion by controlling OSC3 and coordinate detection
using the pen-down interrupt. Therefore, it is
necessary to enable the pen-down interrupt before
starting pen-down check.
The pen-down check is invalid during coordinate
detection (RST register = "1").
The pen-down detector has a built-in noise rejecter
at the input line in order to prevent unnecessary
pen-down detection due to noise. This circuit can
detect a pen-down when a low-level pulse longer
than one cycle of the OSC1 clock is input.