sx8650 Semtech Corporation, sx8650 Datasheet - Page 42

• Manufacturer Part Number: sx8650
• Description: World?s Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller With 15kv Esd
• Manufacturer: Semtech Corporation

In Figure 37 the host performs a single conversion and uses the interrupt (NIRQ) signal to read the available data. The
clock stretching is not required and the I2C bus is free for other system traffic. Successive reads require the same diagram
The init setup could be a I2C write sequence of:
I2CRegCtrl1 = 0x23 // Interrupt enable, seven samples filtering
I2CRegChanMsk = XCONV // Acquisition of X
5.2. Automatic mode
In automatic mode (RATE > 0) the SX8650 will automatically decide when to start acquisition, sequence all the acquisitions
and alerts the host if data is available for download with a NIRQ. The host will read the channels and the SX8650 will start
again with the next conversion cycle.
The fastest coordinate rate is obtained if the host reads the channels immediately after the NIRQ.
If the host reads faster than the NIRQ rate, I2C clock stretching occurs or invalid qualified data will be returned, see section
[4.6.7]
To not loose data, the SX8650 will not begin conversion before the host read the channels. If after the NIRQ a delay
superior to the sampling period is made by the host to read the channels a slower coordinate rate is obtained.
The interrupts will be always generated if the control CONDIRQ bit (see Table 9) is cleared to ‘0’. In case there is no pen
detected on the screen then the coordinate data will be qualified as invalid, see section [4.6.7]. This result in a regular
interrupt stream, as long as the host performs the read channel commands, independent of the screen being touched or
not.
If the control CONVIRQ bit (see register I2CregStat Table 9) is set to ‘1’ then the interrupts will only be generated if the pen
detect occurred. This result in a regular interrupt stream, as long as the host performs the read channel commands, only
when the screen is touched. When the screen is not touched, interrupts does not occur.
Figure 38 and Figure 39 show the automatic-sequential mode. After the first sample I2C to make the initialization, traffic is
reduced as only I2C reads are required.
ACS Revision V2.15/October 2009
©2009 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
I2C
NIRQ
bias channel
sample channel
convert channel
Figure 37.
init setup
SELECT
channel
single conversion, filtering and interrupt signaling
CONVERT
channel
World’s Lowest Power & Smallest Footprint 4-wire
Resistive Touchscreen Controller with 15kV ESD
Page 41
read x position
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