AD7889 Analog Devices, AD7889 Datasheet - Page 30

• Manufacturer Part Number: AD7889
• Description: Low Voltage Controller for Touch Screens
• Manufacturer: Analog Devices

Specifications of AD7889

• Resolution (bits): 12bit
• # Chan: 6
• Sample Rate: 105kSPS
• Interface: I²C/Ser 2-Wire,Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni Vdd
• Adc Architecture: SAR
• Pkg Type: CSP

AD7879/AD7889
INTERRUPTS
The AD7879/AD7889 have a dual function interrupt output,
INT , as well as a pen-down interrupt, PENIRQ . The INT output
can be configured as a data available interrupt ( DAV ), as an
out-of-limit interrupt ( INT ), or as a GPIO interrupt.
DAV —Data Available Interrupt
The behavior of the interrupt output is controlled by Bit 13 in
Control Register 3. In default mode (Bit 13 = 0), INT operates
as a data available interrupt ( DAV ). When the AD7879/AD7889
finish a conversion or a conversion sequence, the interrupt is
asserted to let the host know that new ADC data is available in
the result registers.
While the ADC is idle or is converting, DAV is high. When the
ADC has finished converting and new data has been written to
the result registers, DAV goes low. Reading the result registers
resets DAV to a high condition. DAV is also reset if a new con-
version is started by the AD7879/AD7889 because the timer
expired. The host should read the result registers only when
DAV is low. To ensure correct operation of the DAV mode
when using the SPI interface, it is necessary to write 0x0000
to Register 0x81 after a set of register reads. This clears the
internal data read signal.
AD7879/
When the on-board timer is programmed to perform automatic
conversions, limited time is available to the host to read the
result registers before another sequence of conversions begins.
The DAV signal is reset high when the timer expires, and the
host should not access the result registers while DAV is high.
INT —Out-of-Limit Interrupt
The INT pin operates as an alarm or interrupt output when
Bit 13 in Control Register 3 (Address 0x03) is set to 1. The
output goes low if any one of the interrupt sources is asserted.
The results of high and low limit comparisons on the AUX,
VBAT, and TEMP channels are interrupt sources. An out-of-
limit comparison sets a status bit in the interrupt register. A
separate status bit for the high limit and the low limit on each
channel indicates which limit was exceeded. The interrupt
sources can be masked by setting the corresponding enable bit
in this register to 1. There is one enable bit per channel.
AD7889
STATUS
DAV
IDLE
BY HOST
SETUP
Figure 35. Operation of DAV Output
CONVERTING
t
CONV
ADC
AVAILABLE
NEW DATA
HOST READS
RESULTS
IDLE
Rev. C | Page 30 of 40
PENIRQ —Pen Interrupt
The pen interrupt request output ( PENIRQ ) goes low whenever
the screen is touched and the PENIRQ enable bit is set to 0
(Control Register 1, Bit 15). When PENIRQ enable is set to 1,
the pen interrupt request output is disabled.
The pen interrupt equivalent output circuitry is shown in
Figure 36. This digital logic output has an internal 50 kΩ pull-
up resistor, so it does not need an external pull-up. The
PENIRQ output idles high, and the PENIRQ circuitry is always
enabled in master mode (ADC mode = 11), except during
conversions.
When the screen is touched, PENIRQ goes low. This generates
an interrupt request to the host. When the screen touch ends,
PENIRQ immediately goes high if the ADC is idle. If the ADC
is converting, PENIRQ goes high when the ADC becomes idle.
The PENIRQ operation for these two conditions is shown in
Figure 37.
SCREEN
SCREEN
PENIRQ
STATUS
PENIRQ
STATUS
ADC
ADC
X–
Figure 37. PENIRQ Operation for ADC Idle and ADC Converting
TOUCHED
TOUCHED
SCREEN
NOT
NOT
TOUCH
Figure 36. PENIRQ Output Equivalent Circuit
ADC IDLE
PENIRQ
DETECTS
TOUCH
PENIRQ
DETECTS
TOUCH
TOUCHED
TOUCHED
X+
Y+
Y–
ENABLE
PENIRQ
ADC IDLE
CONVERTING
V
CC
ADC
RELEASE NOT
DETECTED
PENIRQ
DETECTS
RELEASE
50kΩ
V
CC
ADC IDLE
PENIRQ
DETECTS
RELEASE
TOUCHED
TOUCHED
PENIRQ
NOT
NOT