SX8650 Datasheet, PDF (41/56 Pages) Semtech Corporation – World’s Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD

SX8650
World’s Lowest Power & Smallest Footprint 4-wire
Resistive Touchscreen Controller with 15kV ESD
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
init setup
I2C
bias channel
sample channel
convert channel
CONVERT
channel
POWDLY
settling time
read x position
Read x
Figure 34. Conversion of a channel, no filter
init setup
I2C
bias channel
sample channel
convert channel
CONVERT
channel
POWDLY
settling time
read x position (I2C clock stretched)
I2C clock stretching
Read x
Figure 35. Conversion of a channel, digital filter enabled, clock starching required
5.1.2. SELECT Command
The host can define very long settling times by using the SELECT, CONVERT sequence. The host determines the settling
time for each separate channel by the time interval between issuing the SELECT and CONVERT command. Therefore the
POWDLY timing is not applicable and is ignored.
As soon as the channel is selected the corresponding channel will be biased. The settling time is determined by the interval
between the host issuing the SELECT and the CONVERT commands. The host can proceed with a read channel
command after the CONVERT command. In case the SX8650 is not ready to convert and filter, the clock of the I2C will be
stretched by the SX8650 until data is available and can be read.
Figure 36 shows an example of I2C sequence using the SELECT, CONVERT sequence command. For an X-channel
SELECT, issue the command: 0x80, followed with the corresponding CONVERT command: 0x90. The SX8650 will make
the X-channel data available over the I2C.
init setup
I2C
bias channel
sample channel
SELECT
channel
CONVERT
channel
Host determined
settling time
read x position
Read x
convert channel
Figure 36. Conversion using the SELECT and CONVERT command
ACS Revision V2.15/October 2009
©2009 Semtech Corp.
Page 40
www.semtech.com