ICST MK715R, MK715RTR Datasheet

MK715

Touch Screen Controller

General Description

The MK715 Touch Screen Controller IC provides all the screen drive, Analog to Digital converter (ADC) and control circuits to easily interface to 4-wire analog resistive touch screens. It also includes a general purpose A to D converter and a clock synthesizer.

The IC continually monitors the screen waiting for a touch. In this mode, the supply current is typically 4µA. 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 303 times per second until no further screen touches are detected, at which time the low current mode is resumed.

The device has a general purpose input into the 10-bit ADC, allowing for the measurement of other inputs such as battery voltage. The MK715 can be powered from a

3.3V supply, and uses an inexpensive 32.768kHz watch crystal as the input reference. An internal Phase-Lock Loop clock synthesizer provides the high speed clock for the ADC, and the option to have a clock output to drive other digital chips in the system.

The tiny package is the same body size as the 14 pin SOIC, with 25 mil spacings on the leads.

Features

 Tiny 20 pin SSOP (150 mil body)  4 microamp standby current  Less than 3mA active current at 3.3V, including

screen drive  Touch pressure can be measured  One or two general purpose A to D inputs  On-chip voltage reference  32.768kHz crystal/clock input  MHz clock outputs available  Operates with four wire touch screens  Ratiometric conversion eliminates screen

calibration  Automatic wake up upon screen touch  Programmable conversion rate to a maximum of

303 points per second  3.3V or 5V supply (2.7V version available)  10 bit A/D converter  Full powerdown control  Touch screen is directly driven - no external

transistors are required  A to D Converter guaranteed monotonic  3 or 4 wire serial interface

Applications

 Notebook Computers  Handheld Computers  PDAs  Touch-screen kiosks

MK715RevD020200

Pin Assignment

TOUCH#

YL PL

4 5 6 7 8 9 10

MK715

20 pin SSOP

ICS reserves the right to make changes in the device data identified in this publication without further notice. ICS advises its customers to obtain the latest version of all device data to verify that any information being relied upon by the customer is current and accurate.

20 19 18 17 16 15 14 13 12 11

CLKOUT INT VDD X2 X1 GND CAP2 CAP1 CAP3

MK715

Pin Descriptions

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1KSI .kcolClaireS

2ODO .3nipottcennoc,troplaireseriw3roF.tuOataD

3IDI .2nipottcennoc,troplaireseriw3roF.nIataD

4#HCUOTO .tuokcolClanoitpO.dehcuotsineercsnehwwolseoG.langiShcuoT

5HXST.)edisthgir(neercshcuotnohgih-XottcennoC

6LXST.)edistfel(neercshcuotnowol-XottcennoC

7HYST.)pot(neercshcuotnohgih-YottcennoC

8LYST.)mottob(neercshcuotnowol-YottcennoC

9LPI .tupniCDAesopruplareneG

01PGI .tupniCDAesopruplareneG

113PAC- .dnuorgotroticapacFu10.0atcennoC

211PAC- .noitcennocretlifpooL

312PAC- .noitcennocretlifpooL

41DNGP .dnuorgottcennoC

511XI .tupnikcolcrofdnuorgro,latsyrczHk867.23ottcennoC

612XI .tupnikcolcrolatsyrczHk867.23ottcennoC

71DDVP .V3.3+roV5+ottcennoC

81TNIO .tuptuokcolclanoitpO.tpurretnilangisothgihseoG.tpurretnI

91TUOKLCO .tuptuozHMeboslanaC.zHk867.23yllacipyT.tuptuokcolC

02SCI .hgihevitcAtcelespihC

Key: I = Input, O = Output, I/O = Input and Output, P = Power, TS = Touch Screen pin.

MK715

Chip Overview

The MK715 communicates via a 4 pin serial port. This may be connected as either a 3 or 4 wire serial port. The port is connected to 4 registers that control the various modes and function of the chip.

The primary function of the MK715 is to control resistive touchscreens. There are two ways to read screen points, both controlled by the registers.

In the first method, which is enabled by setting the ENCONR bit, the MK715 performs periodic conversions at a rate set by the rate register. The chip monitors the touch screen in a low power condition (about 4 mA) until the screen is touched. When a touch is detected, the chip powers up and starts converting screen points. The TOUCH# pin goes low and INT goes high to indicate a change in touch status. The converter outputs a Y co-ordinate, then an X co-ordinate, then a Y coordinate, and so on. The X and Y co-ordinates are stored in the same register (RESULT) and each conversion over-writes the previous conversion. When a co-ordinate is stored, the conversion complete bit is asserted in the STATUS register. This bit is cleared when the RESULT register is read. The inverted state of the TOUCH# pin also appears in the STATUS register. After each coordinate conversion, INT goes high and the screen is checked to see if it is still touched. If not, conversions stop, TOUCH# goes high, INT goes high (to indicate a change in touch status) and the chip reverts to the low power mode.

The second method to read a screen is to set the RD1PT (read one point) bit in the CONTROL register. The chip will perform two conversions, a Y co-ordinate followed by an X co-ordinate. The X co-ordinate overwrites the Y co-ordinate and so the X co-ordinate must be read before this happens. Finally, RD1PT is cleared. The conversion pair takes about 3.5 ms.

The converter may also be used to measure voltages presented on the GP or PL pins. The range of the converter is 0 to 1.279 V and so voltages outside this range must be scaled appropriately. Again, the RD1PT bit is set to start the conversion but first either SELGP or SELPL must be set to select the correct input. Only one conversion is performed. The result is stored in the RESULT register and then RD1PT is cleared. The conversion takes about 1.7ms.

The final conversion mode is used to measure touch pressure. This is controlled identically to the second method outlined above except that either RDPRESA or RDPRESB must first be set.

The MK715 allows for several different clocks to be generated, controlled by the registers. On the CLKOUT pin, the output is either a a 32768 Hz clock from the crystal oscillator or a MHz - frequency clock synthesized from the PLL. Similarly, this MHz - frequency clock can appear on the INT or TOUCH# pins instead of their usual functions. In these cases, if the MHz clock needs to run continuously, then the ENPLL bit must be set in order to override the automatic powerdown of the PLL. Refer to page 12 for more details.

MK715

Block Diagram

Registers

CAP3

CAP1

CAP2

D0 CS

Serial

Port

Voltage

Reference

32.768kHz Oscillator

Status

Rate

Result

Control

Controller

10 Bit A-D

Converter

Phase

Locked

Loop

0 1 2 3

Screen

Drive

1 0

INT

TOUCH#

CLKOUT

XL YH

YL PL

MK715

IC Operation

(Periodic Conversions Enabled)

Power ON

Is screen touched?

Write D6 Reg 0 to 1 and TOUCH# = 0

Issue Interrupt, power-up ADC and PLL

Convert Y co-ordinates

Store Y co-ordinates in Register 2

Write D7 register 0 to 1

Issue interrupt

Is screen touched?

Convert X co-ordinates

Store X co-ordinates in Register 2

Write D7 register 0 to 1

Issue Interrupt

Wait. Duration controlled by Rate Register

Is screen touched?

Write D6 Reg 0 to 0 and TOUCH# = 1

Issue Interrupt, power-down ADC and PLL

MK715

The MK715 has four 12 bit registers. However, only 8 bits in each register can be written (D0-D7). The other 4 bits (D8D11) can never be written and are always read only.The RESULT register contains 2 levels, a read only level and a write only level. Reading this register gives the conversion results. Writing this register changes 4 control bits.

DESCRIPTION

Read and Write

STATUS (ADDRESS 0)

11 10 9 8 7 6 5 34210

RATE (ADDRESS 1)

11 10 9 8 7 6 5 34210

RD1PT. Read one point. Cleared when conversion complete. ENCONR. Enable periodic screen conversions at rate set by RATE register. PD. Power Down. Chip powers down. See CONTROL register bit 7. ENPLL. Overrides automatic powerdown of PLL between conversions and forces continuous running. SELGP. Select GP input to ADC. SELPL. Select PL input to ADC. Touch Status. 1 = touch. Conversion complete. Cleared on next read of RESULT register. Always set to zero.

Controls frequency of screen conversions when periodic conversions are enabled. Always set to zero.

TYPE

R/W

R/W R/W

RO RO

R/W

Power-up

State

0 0 0 0

Read

Write

RESULT (ADDRESS 2)

11 10 9 8 7 6 5 34210

RESULT (ADDRESS 2)

11 10 9 8 7 6 5 34210

10-bit conversion result. XSEL. Screen conversion status. 0 = Y coordinate, 1 = X coordinate. Conversion type. 0 = non-screen conversion, 1 = screen conversion.

RDPRESA. Read pressure A. See description of measuring touch pressure. RDPRESB. Read pressure B. See description of measuring touch pressure. PLZERO. Forces PL pin to ground. Can be used to control an external resistor divider. Test mode. ALWAYS WRITE TO 0. Don't Care.

RO RO

X 0

0 X

MK715

DESCRIPTION Read

CONTROL (ADDRESS 3)

11 10 9 8 7 6 5 34210

and Write

SEL0. Clock select 0. See page 11. SEL1. Clock select 1. See page 11. SEL2. Clock select 2. See page 11. SEL3. Clock select 3. See page 11. SEL4. Clock select 4. See page 11. CLKSEL. Clock frequency select. See page 11. 0 = 14.3196 MHz 1 = 14.7456 MHz Set to 0.

DIS32. Determines state of 32.768 kHz oscillator when PD asserted (STATUS register). Always set to zero.

R/W = Read/Write, RO = Read Only, WO = Write Only

Converter Control

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TYPE

R/W R/W R/W R/W R/W R/W

R/W

Power-up

State

0 0 0 0 0 0

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siTP1DR.tnemerusaemerusserp

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hcuotnonoitceseeS.atad

siTP1DR.tnemerusaemerusserp

The converter must be sequenced correctly - before writing RD1PT to one, the appropriate bit (e.g. SELGP) must first be set in a previous write. Only the combinations shown above are permitted. Other combinations will give unpredictable behavior.

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