AD7877 Analog Devices, AD7877 Datasheet - Page 21

• Manufacturer Part Number: AD7877
• Description: Touch Screen Controller
• Manufacturer: Analog Devices

Specifications of AD7877

• Resolution (bits): 12bit
• # Chan: 9
• Sample Rate: 125kSPS
• Interface: Ser
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref),Uni 2.5V
• Adc Architecture: SAR
• Pkg Type: CSP

Data Sheet
Table 6. Codes for Selecting Input Channel and Normal or Ratiometric Conversion
Channel
0
1
2
3
4
5
6
7
8
9
10
-
-
-
-
-
0
1
2
3
4
5
6
7
8
9
10
-
-
-
-
-
CONTROL REGISTER 2
Timer (Control Register 2, Bits[1:0])
The TMR bits in Control Register 2 enable the ADC to
repeatedly perform a conversion or conversion sequence either
once only or at intervals of 512 µs, 1.024 ms, or 8.19 ms. In slave
mode, the timer starts as soon as the conversion sequence is
finished. In master mode, the timer starts at the end of a
conversion sequence only if the screen remains touched. If the
touch is released at any stage, then the timer stops and, the next
time the screen is touched, a conversion sequence begins
immediately.
Table 7. Control Register 2 Timer Selection
TMR1
0
0
1
1
TMR0
0
1
0
1
SER/DFR
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Function
Convert only once (default)
Every 1024 clocks (512 µs)
Every 2048 clocks (1.024 ms)
Every 16,384 clocks (8.19 ms)
CHADD(3:0)
0 0 0 0
0 0 0 1
0 0 1 0
0 01 1
0 1 00
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
10 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
Analog Input
X+ (Y position)
Y+ (X position)
Y− (Z2)
AUX1
AUX2
AUX3
BAT1
BAT2
TEMP1
TEMP2
X+ (Z1)
X+ (Y position)
Y+ (X position)
Y− (Z2)
AUX1
AUX2
AUX3
BAT1
BAT2
TEMP1
TEMP2
X+ (Z1)
Rev. D | Page 21 of 44
Int/Ext Reference (Control Register 2, Bit[2])
If the REF bit in Control Register 2 is 0 (default value), the
internal reference is selected. Buffer any connection made to
V
supply a reference to other circuits). An external power supply
should not be connected to this pin while REF is equal to 0,
because it might overdrive the internal reference. Because the
internal reference is 2.5 V, it operates only with supply voltages
down to 2.7 V. Below this value, use an external reference.
If the REF bit is 1, the V
internal reference is powered down. This overrides any setting
of the PM bits with regard to the reference. An external
reference can then be applied to the REF pin.
REF
X Switches
Off
On
X+ off, X− on
Off
Off
Off
Off
Off
Off
Off
X+ OFF, X− ON
Off
On
X+ off, X− on
Off
Off
Off
Off
Off
Off
Off
X+ off, X− on
while the internal reference is selected (for example, to
Invalid address
Invalid address
Invalid address
Invalid address
Invalid address
Invalid address
Invalid address
Invalid address
Invalid address
Invalid address
REF
Y Switches
On
Off
Y+ on, Y− off
Off
Off
Off
Off
Off
Off
Off
Y+ on Y− off
On
Off
Y+ on, Y− off
Off
Off
Off
Off
Off
Off
Off
Y+ on, Y− off
pin becomes an input and the
+REF
Y+
X+
Y+
V
V
V
V
V
V
V
Y+
V
V
V
V
V
V
V
V
V
V
V
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
REF
AD7877
−REF
Y−
X−
X−
GND
GND
GND
GND
GND
GND
GND
X−
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND