wm9715l Wolfson Microelectronics plc, wm9715l Datasheet - Page 40

• Manufacturer Part Number: wm9715l
• Description: Ac?97 Audio And Touchpanel Codec
• Manufacturer: Wolfson Microelectronics plc

WM9715L
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PRINCIPLE OF OPERATION - FIVE-WIRE TOUCHPANEL
When the touchpanel is not being touched, no current flows in the circuit, and the PENDOWN signal
is low. When the panel is touched with a pen or finger, current flows through R
the comparator output goes high.
The PENDOWN signal can be transmitted through the PENDOWN pin (see “Interrupt Control”
section). Additionally, its state is reflected in the PNDN bit (register 7Ah, bit 15) and the interrupt logic
block (register 54h, bit 13), where it can wake the WM9715L from sleep mode (see “Interrupt Control”
section).
Figure 9 Touch Pressure Measurement on 4-wire Touchpanel
Touch pressure can be determined indirectly by measuring the contact resistance R
top and bottom plates. R
measures R
on each plate. The two values are subtracted in the digital domain to obtain the potential difference,
which is proportional to R
To suit different types of touchpanels, the magnitude of I
the PIL control bit.
Five-wire touchpanels are connected to the WM9715Las follows:
•
•
•
•
•
Figure 10 X Co-ordinate Measurement on 5-wire Touchpanel
Top sheet contact = WIPER/AUX4 (pin 12)
Top left corner of bottom sheet = TL (pin 16)
Top right corner of bottom sheet = TR (pin 15)
Bottom left corner of bottom sheet = BL (pin 17)
Bottom right corner of bottom sheet = BR (pin 14)
C
by sending a constant current I
C
C
.
decreases as the touch pressure on the panel increases. The WM9715L
P
through the touchpanel and measuring the potential
P
can be set to either 400µA or 200µA using
PD Rev 4.0 December 2007
PU
and the panel, and
Production Data
C
between the
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