MK715

MK715 ICST | Alldatasheet

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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. MK715RevD020200 Touch Screen Controller 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. • 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 Pin Assignment

Applications

• Notebook Computers • Handheld Computers • PDAs • Touch-screen kiosks General Description Features MK715 20 pin SSOP CS CLKOUT INT VDD GND CAP2 CAP1 CAP3 SK DI TOUCH# XH XL YH YL PL GP

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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 co- ordinate, 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 co- ordinate 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. Chip Overview

32.768kHz Oscillator

10 Bit A-D

TOUCH# INT PL YL XL XH YH GP CAP3 SK CS DI CAP1 CAP2

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 Issue Interrupt Issue Interrupt, power-down ADC and PLL Is screen touched? Is screen touched? Power ON Is screen touched? Issue interrupt Write D7 register 0 to 1 Y N N N Y Y Convert X co-ordinates Store X co-ordinates in Register 2 Write D7 register 0 to 1 Write D6 Reg 0 to 0 and TOUCH# = 1 IC Operation (Periodic Conversions Enabled) Wait. Duration controlled by Rate Register

The MK715 has four 12 bit registers. However, only 8 bits in each register can be written (D0-D7). The other 4 bits (D8- D11) 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. Register Description

DESCRIPTION

RESULT (ADDRESS 2) RATE (ADDRESS 1) RESULT (ADDRESS 2) STATUS (ADDRESS 0) Read and Write Read and Write Read Write Controls frequency of screen conversions when periodic conversions are enabled. Always set to zero. 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. 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. TYPE R/W R/W R/W R/W R/W R/W RO RO RO Power-up State R/W RO RO RO RO X WO WO WO WO X 11 10 9 8 7 6 5 342 1 0 11 10 9 8 7 6 5 342 1 0 11 10 9 8 7 6 5 342 1 0 11 10 9 8 7 6 5 342 1 0

CONTROL (ADDRESS 3)DESCRIPTION Read 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. TYPE R/W R/W R/W R/W R/W R/W R/W R/W RO Power-up State Converter Control 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. Register Description (cont.) BSERPDRA SERPDRL PLESP GLESR NOCNET P1DRD EMROFREPNOISREVNOC 00 0 0 0 1 ot0 ehtnosnoisrevnoc2smrofreP XnanehtdnaYa-neercs .deraelcnehtsiTP1PR.noisrevnoc 00 0 0 1 0 tessaetartasnoisrevnocelbanE sineercsnehW.retsigerETARni setareporetrevnoc,dehcuot sihcuotonlitnuylsuonitnoc yllacitamotuanehtpihC.detceted .etatsybdnats,rewopwolotseog 00 0 1 0 1 ot0 PGnonoisrevnocenosmrofreP .deraelcsiTP1DR.tupni 00 1 0 0 1 ot0 LPnonoisrevnocenosmrofreP .deraelcsiTP1DR.tupni 01 0 0 0 1 ot0 dnaYa,snoisrevnocowtsmrofreP erusserphcuotevigot,Xnaneht hcuotnonoitceseeS.atad siTP1DR.tnemerusaemerusserp .deraelc 10 0 0 0 1 ot0 dnaYa,snoisrevnocowtsmrofreP erusserphcuotevigot,Xnaneht hcuotnonoitceseeS.atad siTP1DR.tnemerusaemerusserp .deraelc R/W = Read/Write, RO = Read Only, WO = Write Only 11 10 9 8 7 6 5 342 1 0

Rate Register (Register 2) Programming Calculating Points Per Second The formula for determining P.P.S. is: P.P.S. = fin 24072+(4096×COUNT) Where fin is the frequency of the internal clock (14.3196 MHz or

14.7456 MHz) and COUNT is

the value of the rate register. On application of power, an internal reset is generated that clears all bits in registers 0, 2, and 3. Register 1 is set to 32 giving a rate of 92 PPS with 14.3196 MHz selected. Power-On Reset The interrupt on the MK715 can only be cleared by reading any register or, alternatively, by writing PD (register 0, bit 2) to one, which forces a powerdown. After a fault condition, initialize the MK715 by writing PD to one, then writing PD to zero. This will always clear pending interrupts. Initializing the MK715 5ot0d ettimreptoN5 27 115 80 4 63 036 23 110 98 3 70 827 29 015 96 3 89 528 26 010 014 3 92 429 23 015 012 3 017 220 30 010 111 3 113 121 38 95 110 3 211 022 35 90 219 2 311 913 33 95 218 2 411 814 30 95 316 2 512 715 38 85 414 2 615 610 48 75 512 2 717 515 41 75 611 2 811 510 54 65 710 2 915 415 59 55 819 1 029 310 65 55 918 1 124 315 61 55 027 1 229 210 77 45 126 1 325 215 75 45 325 1 420 210 82 45 524 1

The serial port has 4 pins - serial clock (SK), chip select (CS), data in (DI), and data out (DO). The SK acts on the rising edge. The CS acts as a reset for the serial port with CS going high initiating a cycle. The cycle consists of 2 parts - a write followed by a read. Each part consists of 12 bits. Refer to the serial port diagram on page 10 and timing diagram on page 20. After CS goes high, any number of leading zeros can occur on DI. When a one is presented (even if this is the first bit after CS goes high), this becomes the start bit. The start bit is followed by 3 op-code bits. The first is a write bit (WR), which determines whether the data following is actually loaded into the appropriate register or not. The next two bits are address bits, which select 1 of 4 on-chip registers. The last 8 bits are data. If WR was low, then these data bits are ignored. On the fourteenth SK rising edge after a start bit, DO is released from tri-state and data is clocked out of the part. This is the read part of the cycle. The register to be read is selected with the op-code address. The data are 12 bits long. For the result of a conversion (which is stored in register 2), this data consists of 10 bits from the ADC, a bit identifying an X or a Y coordinate, and a bit identifying a screen conversion or a general purpose conversion. For the other 3 registers, the data are only 8 bits long, so the 12 bit output word contains four leading zeros. After the 12 data bits are clocked out, the DO pin stays active and bits will continue to appear until CS goes low. See the following page for the timing diagram. Three-Wire Serial Port To configure the serial port for 3 wires, DI must be connected to DO to form a bi-directional data line. All other timing and configuration remain unchanged. Touch Screen Serial Port (Four Wire) The MK715 generates an interrupt to signal a change in touch status or to signal that a conversion is complete. The INT pin (pin 2) goes high to signal an interrupt. Interrupts are then cleared by reading any register. However, if the MK715 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. Interrupts Warning - Operation under a Power Supply Switching Regulator When using the MK715 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 MK715, so it should be disabled when the MK715 is doing screen conversions. Data is written to, and read from, the MK715 via the serial port. When writing, only 8 data bits can be written to each 12 bit register. The 4 highest order bits (D8-D11) in each register are read only and can never be writtern. When reading, all 12 bits are returned.

The GP pin is a general purpose input to the 10 bit ADC. An on-chip 1.297 V reference is used, where 1.297 V is full scale. In addition, when using a 4-wire touch screen, the PL pin is available as a general purpose input, or it can be used as a power control for an external resistor divider: Using the General Purpose Inputs to the A to D Converter For two voltages, the connection is as follows: If PL or GP are unused, they should be connected to ground. The capacitors connected to GP and PL are optional and will reduce noise on the ADC input. ADC Voltage to be measured PLZERO SELGP SELPL ADC PLZERO=0 (transistor off) SELGP SELPL Voltage 1 Voltage 2 SELGP, SELPL, and PLZERO are all register bits. GP GP PL PL MK715 MK715 Optional Capacitor Optional Capacitor

Clocks may be programmed to be on any of three pins per the description above. The clocks are controlled by the following register bits (see register description for more details): STATUS register, bits 2 and 3; and CONTROL register bits 0, 1, 2, 3, 4, 5, 7. 2LESD PL LPNE2 3SIDQ ERFTUOKLCS ETON 00x 0 8 67.23e tatSpu-rewoP 00x 1 8 67.23 01 x 0 8 67.23 01 x 1 F FO 100 x Z HM nehwylnosnuR dehcuotneercs 10 1 x Z HMg ninnuRsyawlA 110 x F FO 111 x F FO CLOCKMHZ Phase Locked 32.768kHz To A-D Converter SEL0, SEL1 / 8 CLKOUT TOUCH# INT CLKSEL ENPLL PD DIS32 PD / 4 / 2 TOUCH# SEL2 SEL4 SEL3 14.3196 or INT LESKC1 LES0 LESZ HMKCOLC 000 6 913.41 001 0 61.7 01 0 0 85.3 011 0 97.1 100 6 547.41 10 1 8 273.7 110 4 686.3 111 2 348.1 2LEST UOKCOLC 0z Hk867.23 1Z HMKCOLC 4LES# HCUOT 0# HCUOT 1Z HMKCOLC 3LEST NI 0T NI 1Z HMKCOLC

The power consumed by the MK715 can be controlled by programming various register bits. DP2 3SIDL LPNER NOCNE neercSehtsI ?dehcuoT noitidnoCpihCD DIlacipyT

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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 MK715. This initiates a conversion, as long as conversions at rate (ENCONR) 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 the current X or Y points have been taken. If the pen is lifted during a conversion, this will also not be detected until the conversion is complete. Pen Bounce TOUCH# INT PL XL XH YH GP SK CS DI GND VDD To Interrupt Controller To Microcontroller To Power Management CAP3 CAP2 CAP1 YL CLKOUT To Touch Screen From Microprocessor 32.768 kHz Crystal + 3.3V or +5V Analog Voltage All 0.01mF 0.01mF 1mF 0.01mF The capacitors connected to CAP1 and CAP3 must be low leakage, ceramic type capacitors. 100kW 0.01mF 470 pF

Optimizing Performance when Reading and Writing Registers Reading and writing the MK715 generates digital noise that may reduce the accuracy of the A to D converter. This noise has several causes, including board layout, and power supply voltage. By appropriately timing the register operations, the effects of this noise can be minimized. After an interrupt is issued or RDIPT is asserted, the MK715 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. 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. 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.

Analog to Digital Converter Operation with a Touchscreen The 10-bit ADC converts X and Y co-ordinates at a rate determined by register 1. 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. 1023) 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 511. 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 up to 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. Full Scale (1023) X Coordinate MK715 XH XL YL Screen Interconnect Screen Interconnect Board and Wire Interconnect Board and Wire Interconnect Screen

When RD1PT is asserted, the converter automatically performs two conversions. The status of the XSEL bit identifies the conversions. The following table gives the four measurements available. From these four measurements, the resistance of the touch can be calculated as a proportion of x-plate and y-plate resistance. See the next section for suggestions about calculating the touch resistance. From this, the touch pressure can be inferred. See the table on page 7 for the correct register sequencing of the converter. Measuring Touch Pressure Measuring touch pressure can only be performed on 4-wire touchscreens. In normal operation, the screen drivers force XH high and XL to ground and measure the voltage on the other plate. A schematic of this is as follows: Voltage measured on YH is now the voltage at L. Voltage measured at XL is now the voltage at K. The difference is proportional to the touch pressure. Voltage measured on YH is the same as at K and L giving the X co-ordinate. When RDPRESA is asserted, the screen drive changes as follows (XSEL=1): Both points returned in one conversion pair. Both points returned in one conversion pair. BSERPDRA SERPDRL ESXE VIRDD ERUSAEMNIP 01 0 L X,HYH X

011 L Y,HXH Y

100 L X,HYL Y

10 1 L Y,HXL X

RTOUCH = RX • • ( - 1) where R X = X plate resistance Calculating Touch Resistance There are a total of six measurements possible: where the result is a number from 0 to 1023. From simple network theory, RTOUCH can be represented in many ways, 3 are given below: or RTOUCH = RY • • ( - 1) where R Y = Y plate resistance or RTOUCH = • • (1023 - E) - RY + D 1023 G E C 1023 H F RY • C 1023 D 1023 RX E BSERPDRA SERPDRL ESXE VIRDD ERUSAEMNIPT LUSER

000 L Y,HYH XC

001 L X,HXH YD

01 0 L X,HYH XE

011 L Y,HXH YF

100 L X,HYL YG

10 1 L Y,HXL XH

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B SK High TIme 15 (SK Period) -15 ns C CS Setup to SK high 15 ns D DI Setup to SK high 15 ns E DI Hold from SK high 15 ns F DO valid from SK high 20 ns G CS hold from last SK high 50 ns MK715 TIMING DIAGRAM 1 234 A B SK WR A1 CS DI C ED DO Tri-State 14 15 16 25 D11 D10 D9 D1 D0 Don't Care SK CS DI DO F F G

Notes: 1. All digital signals should be kept well away from pins 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16 and any traces connected to those pins. Pin 1 G G G G V 32768 Hz0.01mF 0.01mF 0.01mF 0.01mF G V 100kW 1000 pF To Touch Screen = Connection to ground plane = Connection to VDD plane

Package Outline and Package Dimensions

Ordering Information

Integrated Circuit Systems, Inc.• 525 Race Street • San Jose •CA•95126 • (408)295-9800tel • www.icst.com 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 pin SSOP ( in inches) rebmuNredrO/traPg nikraMg nippihS R517KMR 517KMs ebuT RTR517KMR 517KMl eeRdnaepaT lobmySn iMx aM A3 50.09 60.0 1A4 00.00 10.0 B8 00.02 10.0 C7 00.00 10.0 D7 33.04 43.0 E0 51.07 51.0 eC SB520.0 H8 22.04 42.0 L6 10.00 50.0 L B A1 C L (For current dimensional specifications, see JEDEC Publication No. 95.)