SX8652ICSTRT Semtech, SX8652ICSTRT Datasheet - Page 27

• Manufacturer Part Number: SX8652ICSTRT
• Description: 4/5-wire Resistive Touch Screen Controller (SPI)
• Manufacturer: Semtech

8. Application Information
This section describes in more detail application oriented data.
8.1. Acquisition Setup
Prior to an acquisition, the SX8652 can be setup by writing the control registers. Registers are written by issuing the
register write command. They can be read by issuing the read command. Please refer to the section [6.3].
If no registers are written, the circuit will start in manual mode.
8.2. Channel Selection
The SX8652 can be setup to start a single channel conversion or to convert several channels in sequence. For a single
conversion, the channel to be converted is determined from the CHAN(2:0) field in the command word (defined in
Table 11).
Several channels can be acquired sequentially by setting the CHAN(2:0) field to SEQ. The channels will be sampled in the
order defined by register RegChanMsk from MSB to LSB.
If a “one” is written in a channel mask, the corresponding channel will be sampled, in the opposite case, it is ignored and
the next selected channel is chosen.
8.3. Noise Reduction
A noisy environment can decrease the performance of the controller. For example, an LCD display located just under the
touch screen can adds a lot of noise on the high impedance A/D converter inputs.
8.3.1. POWDLY
In order to perform correct coordinates acquisition properly, some time must be given for the touch screen to reach a
proper level. It is a function of the PCB trace resistance connecting the SX8652 to the touchscreen and also the
capacitance of the touchscreen. If tau is this RC time constant then POWDLY duration must be programmed to 10 tau to
reach 12 bit accuracy.
Revision V1.6/July 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
All conversion
All channel
data read
Start channel conversion
finished
Touch Detected ?
PENTRIG MODE
Release Interrupt
yes
Set interrupt
NIRQ=0
NIRQ=1
Figure 25. PENTRIG Mode Flowchart and SPI working in PENTRIG mode
no
TOUCH
NIRQ
CS
DIN
DOUT
Read Channel Data CMD
15kV ESD Low Power 4-Wire / 5-Wire Resistive
Data from SX8652
Page 27
Conversion time
Touchscreen Controller with SPI Interface
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SX8652