
S1C88409 TECHNICAL MANUAL
EPSON
161
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (Touch Panel Controller)
Deciding drawing speed and getting
coordinates
The touch panel controller performs A/D conver-
sion for getting a coordinate at least 16 times (256
times maximum) each for X and Y, and takes the
arithmetic mean. The mean result is written to the
coordinate data register as the coordinate value.
X coordinate data register: DX11–DX0
(00FFA8HD7–D0, 00FFA9HD3–D0)
Y coordinate data register: DY11–DY0
(00FFAAHD7–D0, 00FFABHD3–D0)
The touch panel controller can generate an inter-
rupt when the detected coordinate values are
written to both the X and Y coordinate data
registers. Thus coordinate values can be read and
processed using the interrupt.
The number of A/D conversions for getting a
coordinate differs depending on the mode de-
scribed below.
(1) Constant-speed mode
The constant-speed mode is set by writing "1" to
the CONST (00FFA0HD4) register.
This mode always performs the same number of
A/D conversions regardless of drawing speed and
takes the mean for detecting one coordinate.
Consequently, the coordinate detection speed is
always constant.
The number of A/D conversions for averaging can
be selected from the five types shown in Table
5.17.3.2 using the AVN register.
Table 5.17.3.2 Number of A/D conversion in constant-
speed mode
AVN2
0
1
AVN1
0
1
×
AVN0
0
1
0
1
×
Number of
A/D conversion
16
×16
16
×8
16
×4
16
×2
16
×1
The set number of A/D conversions are performed
for both the X and Y coordinates.
(2) Normal mode
The normal mode is set by writing "0" to the
CONST register. It is also set at initial reset.
In the normal mode, the hardware changes the
number of A/D conversions according to the
drawing speed. A low-speed drawing increases the
number of A/D conversions, it raises coordinate
detection precision. A high-speed drawing de-
creases the number of A/D conversion, it makes it
easy to track the pen.
The drawing speed is detected by the adder-
subtracter shown in Figure 5.17.3.2 as the approxi-
mation expression.
|(previous X coordinate) - (current X coordinate)|
+ |(previous Y coordinate) - (current Y coordinate)|
Comparator
Adder-
subtracter
Previous
coordinate
Current
coordinate
MVH
Comparator
MVMH
Comparator
MVML
Comparator
MVL
MV3
MV2
MV1
MV0
Fig. 5.17.3.2 Drawing speed judgment circuit
The drawing speed judgment circuit compares the
output from the adder-subtracter with the follow-
ing four threshold values to decide the number of
A/D conversions for the next coordinate detection.
MVH (00FFA5HD7–D4):
Threshold value for
high-speed judgment
MVMH (00FFA5HD3–D0): Threshold value for
middle-high-speed
judgment
MVML (00FFA4HD7–D4): Threshold value for
middle-low-speed
judgment
MVL (00FFA4HD3–D0):
Threshold value for
low-speed judgment