SX8652ICSTRT Semtech, SX8652ICSTRT Datasheet - Page 25

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

7.1. Manual Mode
In manual mode (RATE=0) single actions are triggered by the SPI commands described in Table 14.
When a command is received, the SX8652 executes the associated task and waits for the next command. It is up to the
host to sequence all actions.
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.
7.2. Automatic mode
Figure 22. AUTO Mode Flowchart
Revision V1.6/July 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
All conversion
Timer expire
All channel
data read
Start channel conversion
finished
Touch Detected ?
Release Interrupt
Set timer=RATE
yes
Set interrupt
Start timer
NIRQ=0
NIRQ=1
yes
Command
CONVERT(CHAN)
SELECT(CHAN)
CONDIRQ=1 ?
AUTO MODE
no
Table 14.
In automatic mode (RATE > 0), SX8652 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 SX8652 will
start again with the next conversion cycle.
The fastest coordinate rate is obtained if the host reads the channels
immediately after the NIRQ.
To not loose data, the SX8652 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.
When the control CONDIRQ bit (see register RegStat Table 13) 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 [6.1.5]. 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.
This working is illustrated in Figure 22.
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 25
Touchscreen Controller with SPI Interface
Action
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