ICST MK712SITR Touch screen controller Datasheet

MK712
Touch Screen Controller
I C R O C LOC K
Description
Features
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.
• Fully integrated, lowest power solution
• Low standby current of 0.5µA (typical) at 5.0V
• Active current while converting less than 10 mA
• Resolves 350 dots/inch on 10.5” display
• Maximum speed of 197 points/second
• Ratiometric conversion may eliminate screen
calibration
• Automatically wakes up and goes back to standby
• 3.3V or 5V 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
• See the MK715 for a serial interface
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.
Block Diagram
8
D0-D7
A0-A2
3
CS
RD
WR
CLKIN
(14.318 MHz)
INT
TOUCH
REGISTERS
STATUS LOW
STATUS HIGH
X-LOW
X-HIGH
Y-LOW
Y-HIGH
CONTROL
RATE
12 Bit A/D,
Screen Driver
and
Controller
0
1
2
3
4
5
6
7
Pin Assignment
XH
XL
YH
YL
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
1
Revision 100899 Printed 11/16/00
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MDS 712 I
I C R O C LOC K
MK712
Touch Screen Controller
Pin Descriptions
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
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
Type
O
O
P
P
TS
TS
TS
TS
P
P
I
I
I
I
I
I
I
I/O
I/O
P
P
I/O
I/O
I/O
I/O
I/O
I/O
Description
No Connect
Interrupt. Goes high to signal an interrupt. Cleared on next read.
Touch signal. Goes low when screen is touched. Goes high when not touched.
Connect to +5V or +3.3V.*
Connect to +5V or +3.3V.*
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 a MicroClock clock synthesizer.
Data bit 7.
Data bit 6.
Connect to ground.
Connect to +5V or +3.3V.*
Data bit 5.
Data bit 4.
Data bit 3.
Data bit 2.
Data bit 1.
Data bit 0.
Key: I = Input, O = Output, I/O = Input and Output, P = Power, TS = Touch Screen pin..
*Note: All VDD’s must be connected to the same voltage.
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.
2
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
IC Operation
(Periodic Conversions Enabled)
Power ON
N
Is
Screen
Touched?
Y
Write D4, D5 Reg 0 And
D2, D3 Reg 1 To 1
Issue Interrupt
(If Enabled)
Convert
Y Co-Ordinates
Store Y Co-Ordinates In
Reg 4 and Reg 5
Convert
X Co-Ordinates
Store X Co-Ordinates in
Reg 2 and Reg 3
Write D7 Reg 0 To 1
Issue Interrupt
(If Enabled)
Y
Is
Screen
Touched?
N
Write D4, D5 Reg 0 And
D2, D3 Reg 1 To 0
Issue Interrupt
(if Enabled)
3
Revision 100899 Printed 11/16/00
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
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:
STATUS LOW (0 READ)
7
6
5
4
3
2
1
Y-HIGH (5 READ)
0
7
6
5
4
3
2
1
0
Always zero
1 = touch
Always zero
1 = conversion complete,
cleared on Y-HIGH read
NOTE: When the screen is touched bits 4 and 5,
register 0, and bits 2 and 3 of register 1 are all set to one.
High order bits of Y co-ordinate
Always zero
CONTROL (6 R/W)
7
6
5
4
3
2
1
0
1 = enable interrupts
1 = interrupt on conversion
complete ( if bit 0 = 1)
1 = interrupt on change in
touch status (if bit 0 = 1)
STATUS HIGH (1 READ)
7
6
5
4
3
2
1
0
Always zero
1 = touch
Always zero
1 = interrupt on change in
touch status (if bit 0 = 1)
1 = enable periodic conversions at
rate indicated by RATE register
1 = read one point. Cleared when
conversion complete. Only functions
when bit 4 = 0
0 = powerdown (PD). Conversions,
interrupts and TOUCH output disabled
1 = powerdown (PD). Conversions,
interrupts and TOUCH output
disabled.
X-LOW (2 READ)
7
6
5
4
3
2
1
0
Low order bits of X co-ordinate
NOTE: Bits 2 or 3 and bits 6 or 7 are logically OR’d. For
example writing bit 2 or bit 3 to a one will enable interrupts
on change in touch status.
X-HIGH (3 READ)
7
6
5
4
3
2
1
0
High order bits of X co-ordinate
Always zero
RATE (7 R/W)
7
6
5
4
3
2
1
5
4
3
2
1
0
Count controls frequency of
conversion when periodic
conversions are enabled. See
table on page 5.
Y-LOW (4 READ)
7
6
0
Low order bits of Y co-ordinate
4
Revision 100899 Printed 11/16/00
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Rate Register (Register 7) Programming
Count
P.P.S.
Count
P.P.S.
Count
P.P.S.
0 to 8
Not Permitted
28
95
100
32
9
197
29
93
105
31
10
187
30
90
110
29
11
177
31
88
115
28
12
169
32
86
120
27
13
161
33
84
125
26
14
154
34
82
130
25
15
147
35
80
135
24
16
141
40
72
140
24
17
136
45
65
145
23
18
131
50
60
150
22
19
126
55
55
155
21
20
122
60
51
165
20
21
118
65
47
175
19
22
114
70
44
185
18
23
110
75
42
195
17
24
107
80
39
205
16
25
104
85
37
225
15
26
101
90
35
235
14
27
98
95
34
255
13
P.P.S. = Points Per Second. With a 14.318 MHz clock.
Calculating Points Per Second
The formula for determining P.P.S. is:
P.P.S. =
fin
35716 + (4096 x COUNT)
Where fin is the frequency
of the CLKIN input.
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.
5
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Recommended Circuit
RD
CS
WR
A0 - A2
D0 - D7
From
Microprocessor
CLKIN
14.318 MHz
+3.3V or +5V
22µF
VDD
VDD
VDD
0.1µF
TOUCH
INT
To Power Management
To Interrupt Controller
XH
X HIGH
XL
X LOW
YH
Y HIGH
YL
Y LOW
To
Touch
Screen
0.1µF
GND
GND
GND
0.01µF 0.01µF 0.1µF 0.1µF
Pen Bounce
When the screen is untouched, the Y plate is driven high and the X plate is driven low. When the screen is
touched, the X plate is pulled high, which is detected by the MK712. This initiates a conversion (as long as
periodic conversions are enabled). Some de-bounce is provided by the time constant of the screen
decoupling capacitors combined with the screen resistance. However, once conversions have started, pen
bounce will not be detected until after both the X and Y points have been taken.
If the pen is lifted during a conversion, this will also not be detected until the conversion is complete. This is
typically indicated by a point with the correct Y coordinates, but minimum (for that screen) X coordinates.
Screen Decoupling
The component values suggested should give excellent results. However, for screens with a high
resistance operating at a high conversion rate, extra interrupts may be issued. This is because the time
constant of the screen decoupling capacitors and screen resistance is high, resulting in the screen
appearing to be untouched and then touched between conversions. These extra interrupts can be
eliminated by reducing the size of the screen decoupling capacitors on pins XH, XL, YH, and YL.
This will, however, slightly reduce the noise rejection, which could decrease the accuracy of the
conversion.
6
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Optimizing Performance when Reading and Writing Registers
Reading and writing the MK712 generates digital noise that may reduce the accuracy of the A to D
converter. This noise has several causes, including board layout, data bus loading, and power supply
voltage. By appropriately timing the register operations, the effects of this noise can be minimized.
After an interrupt is issued, the MK712 allows a minimum of 1 millisecond to elapse before
initiating the conversion cycle. This allows the screen drivers to settle. For best performance,
complete all register operations within this 1ms window after an interrupt.
Power Down/Stopping the Clock
If the screen is untouched, the supply current is under 3µA. If the input clock is stopped, the supply
current is also less than 3µA. When the screen is touched with no clock, TOUCH goes low and INT
goes high, but no further operations occur until the clock starts. A to D conversions are invalid until
after the clock has stabilized at the correct frequency and one full conversion cycle has been
completed.
Input Clock
The MK712 is highly tolerant of different clock frequencies (from 12 to 20 MHz), rise times, and
duty cycles. However, any input clock undershoot or overshoot will cause the MK712 to draw extra
current. This can be eliminated by using a MicroClock clock synthesizer and properly terminating
the clock driver. MicroClock makes low power clock synthesizers with 14.3 MHz power down.
Resistive Touch Screen (4 Wire)
Resistive touch screens consist of 2 resistive plates that are separated by a small gap. Each plate has an
electrode at each end and when the screen is touched, the two plates are shorted together at that point.
YH
Y PLATE
X PLATE
Electrode
XL
XH
YL
If a voltage is applied, for example, between XL and XH, then a voltage divider is formed on the X
PLATE. When the Y PLATE is touched to the X PLATE, a voltage will be developed on the Y PLATE
that is proportional to distance of the touch from XL and XH. By accurately measuring this voltage, the
position of the touch can be determined.
7
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Recommended Method for Reading Points
If the user is pressing lightly on the touch screen, it is likely that the screen contact will be intermittent.
The screen will bounce, causing false points. This effect can be reduced by insuring that the screen is
touched both before and after a conversion. By doing this, the first and last point in a series of points
are discarded. The following algorithm checks that a point has valid touches both before and after a
conversion, and it distinguishes between change-in-touch interrupts and conversion complete
interrupts. Register 6 bits 0, 1, and 2 must all be true (logical 1) in order to use this method.
Start
Wait for Interrupt
Interrupt
Read Register 0 D7D5, store as D7D5(n)
Read X and Y, store as point n
Increment
n
No
Is D7D5(n-1) = 11b
and D7D5(n) =11b?
Are this point and the previous point valid?
(11b = binary 11)
Yes
Write point n-1 to display
Write previous point.
Warning - When Using a Switching Regulator Power Supply
When using the MK712 in a system where the power is supplied by a switching regulator, do not
perform screen conversions when the regulator is operating in the power saving mode. Some switching
regulators feature a low power mode (for example, Linear Technology’s “Burst Mode”) where the
output is turned on and off in order to save power. The extra power supply noise generated when using
this mode causes spurious data points to be returned from the MK712, so it should be disabled when
the MK712 is doing screen conversions.
8
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Analog to Digital Converter Operation
The 12-bit ADC converts X and Y co-ordinates at a rate determined by registers 6 and 7. The
converter uses a ratiometric technique to give absolute co-ordinates on the screen, largely independent
of variations in screen resistance, temperature or power supply voltage. The total voltage applied across
the screen is defined as full-scale for the converter (i.e. 4095) and any point touched on the screen is
proportional to this. For example, if the screen is touched exactly in the center, the converter will read
2047. This feature may allow for the elimination of calibration upon startup.
However, the full scale voltage is defined at the IC pins and so any parasitic interconnect resistance will
be included in full scale. In addition, the interconnect resistances on the screen also account for about
20% of the total resistance. This means that approximately the bottom 10% and top 10% of full scale
are inaccessible.
The converter is guaranteed to be monotonic, with no missing codes.
BOARD AND WIRE
INTERCONNECT
XH
SCREEN
INTERCONNECT
FULL
SCALE
(4095)
MK712
YL
SCREEN
X
CO-ORDINATE
XL
SCREEN
INTERCONNECT
BOARD AND WIRE
INTERCONNECT
9
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MDS 712 I
I C R O C LOC K
MK712
Touch Screen Controller
Electrical Specifications
Parameter
Conditions
Minimum
Typical
Maximum
Units
7
VDD+0.5
70
260
150
V
V
°C
°C
°C
5.5
V
V
V
V
V
V
V
V
V
V
mA
mA
µA
µA
µA
mA
pF
ABSOLUTE MAXIMUM RATINGS (note 1)
Supply voltage, VDD
Inputs and Clock Outputs
Ambient Operating Temperature
Soldering Temperature
Storage temperature
Referenced to GND
Referenced to GND
-0.5
0
Max of 20 seconds
-65
DC CHARACTERISTICS
Operating Voltage, VDD
Input High Voltage, VIH
Input Low Voltage, VIL
Output High Voltage, VOH
Output High Voltage, VOH
Output Low Voltage, VOL
Input High Voltage, VIH
Input Low Voltage, VIL
Output High Voltage, VOH
Output Low Voltage, VOL
Operating Supply Current, IDD, at VDD=5V
Operating Supply Current, IDD, at VDD=3.3V
Operating Supply Current, IDD standby, clock
Operating Supply Current, IDD standby
Operating Supply Current, IDD power down
Short Circuit Current
Input Capacitance
VDD=5V
VDD=5V
IOH=-2mA
VDD=5V, IOH=-12mA
VDD=5V, IOL=12mA
VDD=3.3V
VDD=3.3V
VDD=3.3V, IOH=-6mA
VDD=3.3V, IOL=6mA
300 Ω screen, 100 PPS
note 4
note 5
note 6
PD=0 or PD=1, no clock
Each output
3.0
2.0
0.8
VDD-0.4
2.4
0.4
1.9
0.4
2.4
0.4
5
3
0.5
0.5
0.2
±50
7
3
3
3
AC CHARACTERISTICS
Input Clock Frequency, pin 18
Input Clock Duty Cycle, pin 18
Output Rise Time
Output Fall Time
Resolution
Non-linearity
Touch Screen Resistance
Note 2
at 1.5V
0.8 to 2.0V, VDD=5V
2.0 to 0.8V, VDD=5V
12
25
Monotonic, note 3
100
14.32
20
75
3
3
12
±2
2000
MHz
%
ns
ns
bits
LSB
Ω
Notes: 1. Stresses beyond those listed under Absolute Maximum Ratings could cause permanent damage to the device. Prolonged
exposure to levels above the operating limits but below the Absolute Maximums may affect device reliability.
2. Consult MicroClock about the best device to use to generate the input clock.
3. With no missing codes.
4. Assumes no 14.3MHz input clock overshoot, 300 Ω screen, 100 PPS
5. Assumes no 14.3MHz input clock overshoot, no touch
6. With no touch, no clock
10
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Register Interface Timing
#
Symbol
Description
Min
Max
Unit
Note
READ AND WRITE CYCLES
1
2
3
TRASC
TRAHC
TRCCY
Address Setup to CS Low
Address Hold from CS High
CS High to CS Low
5
0
40
ns
ns
ns
10
40
0
40
ns
ns
ns
ns
ns
ns
ns
ns
READ CYCLE ONLY
4
5
6
7
8
9
10
11
TRSCR
TRRD
TRCHR1
TRCHR2
TRDC
TRDR
TRDHC
TRDHR
CS Low to RD Low
RD Pulse Width
RD High to CS High
RD High to CS Low
CS Low to Data
RD Low to Data
CS High to Data Release
RD High to Data Release
2
2
35
35
20
20
1
1
WRITE CYCLE ONLY
12
13
14
15
16
17
18
19
20
TRCSW
TRWR
TRCHW
TRWH
TRWCY
TRDW
TRDHW
TRDWC
TRDHWC
Notes:
CS Low to WR Low
WR Pulse Width
WR High to CS High
WR High to CS Low
WR High to WR Low
Data Setup to WR High
Data Hold from WR High
Data Setup to CS High
Data Hold from CS High
10
40
0
40
40
15
15
15
15
ns
ns
ns
ns
ns
ns
ns
ns
ns
2
3
4
3
4
1. RD edges may precede or follow CS edges.
2. WR edges may precede or follow CS edges.
3. Either TRDW or TRDWC specification must be met.
4. Either TRDHW or TRDHWC specification must be met.
5. It is not permitted to have both RD and WR low at the same time.
11
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Register Read
A0 - A2
1
2
CS
3
RD
4
6
5
7
10
9
D0 - D7
8
11
Register Write
A0 - A2
1
2
CS
3
WR
12
13
14
15
16
D0 - D7
17
19
18
20
12
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
12
MK712 Power Supply Current vs. Touchscreen Resistance
VDD=3.3V
10
8
IDD
(mA)
6
4
197 points per second
147 points per second
86 points per second
13 points per second
2
0
100
1000
10000
Touchscreen Resistance (Ω)
Graph 1
18
16
14
12
MK712 Power Supply Current vs. Touchscreen Resistance
VDD=5V
MK712 Power Supply Current vs. Touchscreen Resistance
Vdd= 5 V
IDD 10
(mA)
8
6
4
197 points per second
147 points per second
86 points per second
13 points per second
2
0
100
1000
Touchscreen Resistance (Ω)
10000
Graph 2
13
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
MK712 Power Supply Current vs. Conversion Rate
Screen Resistance = 320Ω
9
8
VDD=5V
7
IDD 6
(mA)
5
VDD=3.3V
4
3
2
1
0
0
50
100
150
200
Conversion Rate (Points Per Second)
Graph 3
14
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
Suggested Layout
22µF
Pin 1
2
3
4
5
G
V
0.1µF 0.1µF
0.01µF
6
7
To
Touch
8
9
Screen
0.01µF
0.1µF
G
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
V
G
0.1µF
G = connection to ground plane
V = connection to VDD plane
Notes:
1. The 14.318 MHz input clock on pin 18 should have a 33Ω series termination resistor at its source.
Consult MicroClock for the best way to generate this clock.
2. All digital signals should be kept well away from pins 4, 5, 6, 7, 8, 9, 10, and 11, and any traces
connected to those pins.
15
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MDS 712 I
MK712
Touch Screen Controller
I C R O C LOC K
28 pin SOIC wide
Package Outline and Package Dimensions
E
Symbol
A
b
c
D
E
H
e
h
Q
H
A
c
Q
e
Millimeters
Min
Max
2.3368 2.6416
0.356
0.483
0.229
0.305
17.678 18.085
7.366
7.620
10.008 10.643
1.27 BSC
0.406
0.076
0.279
28 pin SSOP (QSOP)
h x 45°
D
Inches
Min
Max
0.092 0.104
0.014 0.019
0.009 0.012
0.696 0.712
0.290 0.300
0.394 0.419
.050 BSC
0.016
0.003 0.011
b
Ordering Information
Symbol
A
b
c
D
E
H
e
h
Q
Part/Order Number
Marking
Package
Temperature
MK712S
MK712STR
MK712SI
MK712SITR
MK712R
MK712RTR
MK712RI
MK712RITR
MK712S
MK712S
MK712SI
MK712SI
MK712R
MK712R
MK712RI
MK712RI
28 pin SOIC
Add tape and reel
28 pin SOIC
Add tape and reel
28 pin SSOP
Add tape and reel
28 pin SSOP
Add tape and reel
0 to +70°C
0 to +70°C
-30 to +70°C
-30 to +70°C
0 to +70°C
0 to +70°C
-30 to +70°C
-30 to +70°C
Millimeters
Min
Max
1.55
1.73
0.203 0.305
0.190 0.254
9.780 10.160
3.810 4.064
5.840 6.223
0.635 BSC
0.410
0.127 0.254
While the information presented herein has been checked for both accuracy and reliability, Integrated Circuit Systems, Incorporated (ICS) assumes no responsibility for either its
use or for the infringement of any patents or other rights of third parties, which would result from its use. No other circuits, patents, or licenses are implied. This product is
intended for use in normal commercial applications. Any other applications such as those requiring special processing, high reliability, or other extraordinary environmental
requirements are not recommended without additional processing by ICS. ICS reserves the right to change any circuitry or specifications without notice. ICS does not authorize or
warrant any ICS product for use in life support devices or critical medical instruments.
©1995 ICS/MicroClock
16
Revision 100899 Printed 11/16/00
Integrated Circuit Systems, Inc.•525 Race St.•San Jose•CA•95126•(408)295-9800tel•www.icst.com
MDS 712 I