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ADS7843 PEN INTERRUPT
By Ken Dietz
The ADS7843 is a 12-bit sampling analog-to-digital con-
verter (ADC) used to drive 4-wire touch-screens to serial
interfaces by ratiometrically converting two differential in-
put signals. The ADS7843 also produces an accurate output
with the first conversion cycle once powered up. Because of
this feature, the ADC can be powered up and down continu-
ously, thus, enabling designers to conserve energy in low
power applications such as Personal Digital Assistants (PDA),
where the number of conversions is limited but a fast and
accurate response is required on the first conversion. To
maximize energy conservation, the ADS7843 incorporates a
Pen Interrupt Request feature (PENIRQ), which enables
designers to fully control the power-down operation when
interfacing with Micoprocessors (MPU). Figure 1 is a sim-
plified flow diagram for a PDA showing how PENIRQ is
used to assist in controlling power-down operations.
Sanity
MPU sends byte to
ADS7843 (PD0 = PD1 = 0)
No
ADS7843 powered-down
and PENIRQ enabled
Is pen writing?
Yes
MPU processes data
PENIRQ at high voltage
MPU pulls PENIRQ LOW, writes
to ADS7843 to initiate conversion
Pen depresses touch-screen
MPU senses low voltage
and wakes up
PENIRQ pulled LOW
(typically 0.65V)
FIGURE 1. Simplified Flow Diagram for PDA.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user鈥檚 own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
漏
1998 Burr-Brown Corporation
AB-142A
Printed in U.S.A. April, 1999
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