DATASHEET
TOUCH SCREEN CONTROLLER
Description
The MK712 Touch Screen Controller IC provides all the
screen drive, A to D converter and control circuits to easily
interface to 4-wire analog resistive touch screens.
The IC continually monitors the screen waiting for a touch.
In this mode, the supply current is typically 0.5µA. When
the screen is touched, the IC performs analog to digital
conversions to determine the location of the touch, stores
the X and Y locations in the registers, and issues an
interrupt. This process is repeated up to 197 times per
second until no further screen touches are detected, at
which time the low current mode is resumed.
MK712
Features
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Packaged in 28-pin SSOP (150 mil) or 28-pin SOIC (300
mil)
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Industrial (-30°C to +70°C) and commercial (0 to +70°C)
and automotive (-35°C to +85°C) temperature ranges
Block Diagram
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Pb (lead) free
Fully integrated, lowest power solution
Low standby current of 0.5µA (typical) at 5.0 V
Active current while converting less than 10 mA
Resolves 350 dots/inch on 10.5” display
Maximum speed of 197 points/second
Ratio metric conversion may eliminate screen calibration
Automatically wakes up and goes back to standby
3.3 V or 5 V supply
12 bit A/D converter
Simplifies the writing of software for touch screens
Extended temperature range available
Capacitors are the only external components required
Touch screen is directly driven - no external transistors
are required
Programmable conversion rate
A to D Converter is monotonic
Parallel interface
Pin Assignment
NC
INT
TOUCH
VDD
VDD
XH
XL
YH
YL
GND
GND
WR
RD
CS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
D0
D1
D2
D3
D4
D5
VDD
GND
D6
D7
CLKIN
A0
A1
A2
IDT™
TOUCH SCREEN CONTROLLER
1
MK712
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MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Pin Descriptions
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Pin
Name
NC
INT
TOUCH
VDD
VDD
XH
XL
YH
YL
GND
GND
WR
RD
CS
A2
A1
A0
CLKIN
D7
D6
GND
VDD
D5
D4
D3
D2
D1
D0
Pin Type
—
Output
Output
Power
Power
Touch Screen Pin
Touch Screen Pin
Touch Screen Pin
Touch Screen Pin
Power
Power
Input
Input
Input
Input
Input
Input
Input
I/O
I/O
Power
Power
I/O
I/O
I/O
I/O
I/O
I/O
Pin Description
No connect. Do not connect this pin to anything.
Interrupt. Goes high to signal an interrupt. Cleared on next read.
Touch signal. Goes low when screen is touched. Goes high when not touched.
Power Supply. Connect to +5 V or +3.3 V. (Connect all VDDs to same voltage)
Power Supply. Connect to +3.3 V.
Connect to X-high on touch screen. (Right side)
Connect to X-low on touch screen. (Left side)
Connect to Y-high on touch screen. (Top)
Connect to Y-low on touch screen. (Bottom)
Connect to ground.
Connect to ground.
Write enable. Active low.
Read enable. Active low.
Chip select. Active low.
Register address 2.
Register address 1.
Register address 0.
Clock input. Typically 14.3 MHz. Best if driven by an IDT clock synthesizer.
Data bit 7.
Data bit 6.
Connect to ground.
Power Supply. Connect to +5 V or +3.3 V. (Connect all VDDs to same voltage)
Data bit 5.
Data bit 4.
Data bit 3.
Data bit 2.
Data bit 1.
Data bit 0.
Interrupts
Interrupts are controlled by register 6 (see Register Description). The INT pin (pin 2) goes high to signal an
interrupt. Interrupts are then cleared by reading any register. However, if the MK712 is in the process of generating
an interrupt during a read cycle, then the interrupt is not cleared and INT will stay high. This internal process may
take 100ns, and so to guarantee that the interrupt is cleared, two successive read cycles may be necessary.
IDT™
TOUCH SCREEN CONTROLLER
2
MK712
REV N 051310
MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
IC Operation
IDT™
TOUCH SCREEN CONTROLLER
3
MK712
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MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Register Description
The MK712 register set is designed to be compatible with the Gazelle pen digitizer registers allowing a software
driver for the Gazelle digitizer to be used with the MicroClock MK712. The eight 8-bit registers are defined below:
IDT™
TOUCH SCREEN CONTROLLER
4
MK712
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MK712
TOUCH SCREEN CONTROLLER
TOUCH SCREEN CONTROL
Rate Register (Register 7) Programming
Calculating Points Per Second
The formula for determining P.P.S. is:
Power-On Reset
On application of power, an internal reset is generated that clears all bits in registers 0, 1, and 6. Register 7 is set to
32 giving a rate of 86 PPS. Note that clearing register 6 puts the IC into the power down condition.
Initializing the MK712
The interrupt on the MK712 can only be cleared by reading a register or by writing register 6 to the power down
condition. After a fault condition, initialize the MK712 by writing register 6 to zero and then writing register 6 to the
desired value. This will always clear pending interrupts.
IDT™
TOUCH SCREEN CONTROLLER
5
MK712
REV N 051310
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