
S1C88409 TECHNICAL MANUAL
EPSON
163
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (Touch Panel Controller)
Note: The waiting time to be set using the WAIT
register must be longer than 3 cycles of the
OSC1 clock.
16
× n/f > 3/fOSC1
(
f: Input clock frequency from the
prescaler)
At initial reset, it is set to 16
× 5/f (WAIT="0100B").
(2) Interval time
It is possible to set an interval after an A/D
conversion processing for noise resistance im-
provement, saving power and setting the number
of points to be detected for 1 second.
The interval can be selected from 16 types as
shown in Table 5.17.3.6 using the INV register.
The A/D conversion processing for coordinate
detection performs four A/D conversions at a time.
The set interval is inserted after the processing (four
A/D conversions have finished) and no voltage is
supplied to the touch panel during this period.
Table 5.17.3.6 Interval time setting
IVL3
0
1
IVL2
0
1
0
1
IVL1
0
1
0
1
0
1
0
1
IVL0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Interval time
128
×1/f
128
×2/f
128
×3/f
128
×4/f
128
×5/f
128
×6/f
128
×7/f
128
×8/f
128
×9/f
128
×10/f
128
×11/f
128
×12/f
128
×13/f
128
×14/f
128
×15/f
128
×16/f
f: Input clock frequency from the prescaler
At initial reset, the interval is set to 128
× 3/f
(INV="0010B").
When setting the interval shorter, current con-
sumption will increase and coordinate values
unnecessary for drawing will be detected. Set an
appropriate interval according to the drawing
contents.
Operation of coordinate detection
When "1" is written to the RST register, the touch
panel controller starts operating for coordinate
detection and continues a process as shown in
Figure 5.17.3.4 until "0" is written to the RST
register.
The number of conversions per second while the
pen is tracing on the panel is calculated as an
approximate value by the expression below:
N = 1 / (AV
× 8 (CNT + WAIT + 4 AD + IVL))
AV:
Number of A/D conversions
CNT: 10
× input clock cycle time
(prescaler output clock)
WAIT: WAIT register setting time
AD:
22
× A/D conversion clock cycle
[00FF17HD3–D0]
IVL:
IVL register setting time
Figure 5.17.3.4 shows the operation when the
number of conversions is set to 16
× 1. When a
pen-up is detected in the coordinate conversion
period, the following cycle starts from (1) after
finishing the current cycle. When no pen-up is
detected, the following cycle starts from (2). If the
detected data is regarded as noise, the data register
is not updated.
Pen-down
check
Coordinate
detection 1
Coordinate
detection 2
Coordinate
detection 3
Coordinate
detection 4
Coordinate
detection 5
Coordinate
detection 6
Coordinate
detection 7
Coordinate
detection 8
RST = "1"
(1)
(2)
Pen-down interrupt
Data update interrupt
Pen-down
detection
A/D
conversion 1
Voltage stabilization
waiting time
Charge/discharge
time
A/D
conversion 2
A/D
conversion 3
A/D
conversion 4
Interval
time
Fig. 5.17.3.4 Coordinate detection operation