AD7843ARU-REEL Analog Devices Inc, AD7843ARU-REEL Datasheet - Page 19

• Manufacturer Part Number: AD7843ARU-REEL
• Description: IC ADC 12BIT TOUCHSCREEN 16TSSOP
• Manufacturer: Analog Devices Inc
• Type: Resistiver

Specifications of AD7843ARU-REEL

• Touch Panel Interface: 4-Wire
• Number Of Inputs/keys: 1 TSC
• Resolution (bits): 12 b
• Data Interface: Serial
• Data Rate/sampling Rate (sps, Bps): 125k
• Voltage Reference: External
• Voltage - Supply: 2.2 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP
• Voltage Supply Source: Single Supply
• Sampling Rate (per Second): 125k
• For Use With: EVAL-AD7843EBZ - BOARD EVAL FOR AD7843
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

PEN INTERRUPT REQUEST
The pen interrupt equivalent output circuitry is outlined in
Figure 28. By connecting a pull-up resistor (10 kΩ to 100 kΩ)
between V
PENIRQ output remains high normally. If PENIRQ is enabled
(see Table 7), when the touch screen connected to the AD7843
is touched via a pen or finger, the PENIRQ output goes low,
initiating an interrupt to a microprocessor that can then instruct
a control word to be written to the AD7843 to initiate a conver-
sion. This output can also be enabled between conversions
during power-down (see Table 7 ), allowing power-up to be
initiated only when the screen is touched. The result of the first
touch screen coordinate conversion after power-up is valid,
assuming any external reference is settled to the 12- or 8-bit
level as required.
Figure 29 assumes that the PENIRQ function is enabled in the
last write or that the part has just been powered up, so PENIRQ
is enabled by default. Once the screen is touched, the PENIRQ
output goes low a time t
5 µs, assuming a 10 nF touch screen capacitance, and varies with
the touch screen resistance actually used.
CC
SCREEN
TOUCH
and this CMOS logic open-drain output, the
Figure 28. PENIRQ Functional Block Diagram
Y+
X+
Y–
PENIRQ
DCLK
PEN
ON
TOUCHED
ENABLE
PENIRQ
SCREEN
DIN
CS
HERE
+V
later. This delay is approximately
CC
100kΩ
t
PEN
PROCESSOR
INTERRUPT
+V
CC
EXTERNAL
PULL-UP
PENIRQ
(START)
S
1
A2
Figure 29. PENIRQ Timing Diagram
A1
Rev. B | Page 19 of 20
A0
NO RESPONSE TO TOUCH
MODE
SER/
DFR
Once the START bit is detected, the pen interrupt function is
disabled and the PENIRQ cannot respond to screen touches.
The PENIRQ output remains low until the fourth falling edge
of DCLK after the START bit has been clocked in, at which
point it returns high as soon as possible, regardless of the touch
screen capacitance. This does not mean that the pen interrupt
function is now enabled again because the power-down bits
have not yet been loaded to the control register. Regardless of
whether PENIRQ is to be enabled again or not, the PENIRQ
output normally always idles high. Assuming that the PENIRQ
is enabled again as shown in Figure 29, once the conversion is
complete, the PENIRQ output responds to a screen touch again.
The fact that PENIRQ returns high almost immediately after
the fourth falling edge of DCLK means the user avoids any
spurious interrupts on the microprocessor or DSP, which could
occur if the interrupt request line on the microprocessor/DSP
was unmasked during or toward the end of conversion with the
PENIRQ pin still low. Once the next START bit is detected by
the AD7843, the PENIRQ function is disabled again.
If the control register write operation overlaps with the data
read, a START bit is always detected prior to the end of
conversion. This means that even if the PENIRQ function has
been enabled in the control register, it is disabled by the START
bit again before the end of the conversion is reached; therefore
the PENIRQ function effectively cannot be used in this mode.
However, as conversions are occurring continuously, the
PENIRQ function is not necessary and, therefore, redundant.
GROUNDING AND LAYOUT
For information on grounding and layout considerations for the
AD7843, refer to Application Note AN-577, Layout and
Grounding Recommendations for Touch Screen Digitizers.
1
0
8
1
13
PD1 = 1, PD0 = 0, PENIRQ
ENABLED AGAIN
16
AD7843