SX8650 Datasheet, PDF (46/56 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
X+
Start of the
conversion
5 successive
conversions
POWDLY
SETDLY
time
Figure 41. POWDLY and SETDLY timing with FILT=2
6.3.3. AUX Input
An alternate conversion trigger method can be used if the host system provides additional digital signals that indicate noisy
or noise-free periods. The SX8650 can be set up to start conversions triggered by the AUX pin. A rising edge, a falling
edge or both can trigger the conversion. To enter this mode, AUXACQ must be set to a different value than '00' as defined
in Table 9. The AUX edge will first trigger the bias delay (POWDLY). Following the programmed delay, the channel
acquisition takes place.
6.4. Channel Biasing
The touch screen surface presents a resistive and capacitive load, and therefore the screen bias needs to settle before an
acquisition takes place. In the manual mode, the channels selected are biased when either a SELECT or CONVERT
command is received.
The channel can be biased for an arbitrary amount of time by first sending a SELECT command and then a CONVERT
command once the settling time requirement is met.
The SELECT command can be omitted if the large range of POWDLY settings cover the requirements. In the latter case,
the CONVERT command alone is enough to perform an acquisition.
In the sequential mode, multiple channels are sampled. This requires programming the POWDLY field in register
I2CRegCTRL0. The selected channel will be powered during POWDLY before a conversion is started. The channel bias is
automatically removed after the conversion has completed.
6.5. Interrupt Generation
An interrupt (NIRQ) will be generated:
- during the power-up phase
- after completion of a conversion. CONVIRQ (bit [7] of I2CRegStat) will be set at the same time.
- when a pen detect is triggered, the SX8650 being in pen detect mode. PENIRQ (bit [6] of I2CRegStat) will be set at the
same time.
The NIRQ will be released and then pulled high by the external pull-up resistor:
- when the power-up phase is finished
- the host reading all channels that were previously converted by the SX8650. CONVIRQ, will be cleared at the same time.
- the host reading the I2C status register, the SX8650 being in pen detect mode. PENIRQ, will be cleared at the same time.
ACS Revision V2.15/October 2009
©2009 Semtech Corp.
Page 45
www.semtech.com