SX8652ICSTRT Semtech, SX8652ICSTRT Datasheet - Page 16

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

In the PENDET mode the pen detection is activated. The SX8652 will generate an interrupt (NIRQ) upon pen detection and
set the PENIRQ bit in the SPI status register. To quit the PENDET mode the host needs to configure the manual mode.
In the PENTRG mode the pen detection is activated and a channel conversion will start after the detection of a pen. The
SX8652 will generate an interrupt (NIRQ) upon pen detection and set the CONVIRQ bit in the SPI status register. To quit
the PENTRIG mode the host needs to configure the manual mode. The PENTRG mode offers the best compromise
between power consumption and coordinate throughput.
8.1. MANual Mode
In manual mode (RATE=0), the host sequences all the actions by the SPI commands described in Table 9.
When a command is received, the SX8652 executes the associated task and waits for the next command.
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.
With CHAN=SEQ, multiple channels are sampled. This requires programming the POWDLY field in register RegCTRL0.
The selected channel will be powered during POWDLY before a conversion is started. The channel bias is automatically
removed after the conversion has completed.
8.2. AUTOmatic mode
In automatic mode (RATE > 0), SX8652 start the acquisition when a touch is detected. It converts all the channels selected
with RegChnMsk and set NIRQ low when it is finished.
After the host has read the channels, if CONDIRQ=1 and the touch is detected again, the SX8652 starts a new conversion
cycle.
To not loose data, the SX8652 does not begin conversion before the host read all the channels.
We can define the time ts between the start of the conversion and the end of the channels reading by the host.
The rate programmed is achieved if ts<1/RATE otherwise the new rate is 1/ts.
When the control CONDIRQ bit (see register RegStat Table 15) 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,
and the screen is touched. When the screen is not touched, interrupts does not occur.
If the control CONDIRQ bit is cleared to ‘0’, the interrupts will be always generated. In case there is no pen detected on the
screen then the coordinate data will be qualified as invalid, see section [9.5]. This result in a regular interrupt stream as
long as the host performs the read channel commands,
This working is illustrated in Figure 16.
Figure 14 shows the SPI working in automatic mode with CONDIRQ=1. After the first sentence send through the SPI to
make the initialization, traffic is reduced as only reads are required.
Revision V1.7/October 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
Command
CONVERT(CHAN)
SELECT(CHAN)
Table 9.
CONVERT and SELECT command
Select and bias a channel
Wait for the programmed settling time (POWDLY)
Start conversion
Select and bias a channel
15kV ESD Low Power 4-Wire / 5-Wire Resistive
Page 16
Touchscreen Controller with SPI Interface
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