sx8675iwltrt Semtech Corporation, sx8675iwltrt Datasheet - Page 46

• Manufacturer Part Number: sx8675iwltrt
• Description: Haptics Enabled Multitouch 4/5-wire Resistive Touchscreen Controller With Proximity Sensing
• Manufacturer: Semtech Corporation

ADVANCED COMMUNICATIONS & SENSING
Command
SELECT
CONVERT
MAN
PENDET
PENTRG
11.6 Read Channel (Touchscreen Interface)
The I2C read channel sequence is given in figure below. After the start condition [S], the chip slave address
(SA) is sent, followed by an eighth bit (R=‘1’) indicating a read. The chip responds with an acknowledge [A] and
the first data byte (RD0). The host sends an acknowledge [A] and the chip responds with the second data byte
(RD1). If the host needs to read more channels, it will acknowledge [A] and the chip will send the next data
bytes. This sequence will be repeated until the host terminates with a NACK [N] followed immediately by a stop
[P].
The channel data that can be read is defined by RegChanMsk, or the last convert command in manual mode. A
maximum number of 12 data bytes can be read when all channels (X, Y, Z1, Z2, RX, RY) are activated in
RegChanMsk. The STOP [P] (if following the last valid data) releases high the NIRQ line. All ADC related
operations (touch conversion, proximity conversion, pen detection) are stopped as long as all valid channel data
have not been read (ie as long as NIRQ is low).
The sampling of the screen by the chip and the host I2C bus traffic are events that might occur simultaneously.
The chip will synchronize these events by the use of clock stretching if that is required. The stretching occurs
directly after the address and read bit have been sent for the I2C read channels command (see figure above).
The channel data is sent with the following order: X, Y, Z1, Z2, RX, RY. It is coded as described in figure below
Typical applications require only X and Y coordinates, thus only 4 bytes of data will be read in this case.
Rev 1 – 25
th
July 2011
Command(7:0)
1
1
1
1
1
Channel
X
Y
Z1
Z2
RX
RY
SEQ
0
0
1
1
1
1
1
0
0
1
0
1
0
1
0
Chan(2:0)
0
0
0
0
1
1
1
X
X
X
X
X
0
0
1
1
0
1
1
Figure 56 – I2C Read Channel
X
X
X
Table 10 : Command Codes
0
1
0
1
1
0
1
Chan(2:0)
Chan(2:0)
Table 11 : Channel Codes
X
X
X
Description
X channel
Y channel
First channel for pressure measurement
Second channel for pressure measurement
X multitouch measurement
Y multitouch measurement
Channels enabled in RegChanMsk register
Resistive Touchscreen Controller with Proximity Sensing
X
X
X
46
Function
Select and bias channel.
Convert channel.
Enter manual mode.
Enter pen detect mode.
Enter pen trigger mode.
SX8674/SX8675/SX8676
Haptics Enabled Multitouch 4/5-Wire
www.semtech.com