SEN-09695 - SparkFun Electronics

Document Number: MPR121

Rev. 4, 02/2013

Freescale Semiconductor

Data Sheet: Technical Data

An Energy Efficient Solution by Freescale

Proximity Capacitive Touch

Sensor Controller

The MPR121 is the second generation sensor controller following the

initial release of the MPR03x series of devices. The MPR121 features an

increased internal intelligence plus Freescale ’s second generation

capacitance detection engine. Some major enhanceme nts include an

increased electrode count, a hardware configurable I2C address, an

expanded filtering system with debounce, and comp letely independent

electrodes with built-in autoconfiguration. The device also features a 13th

simulated electrode which represents the simultaneous charging of all the

electrodes connected together. When used with a touch panel or touch

screen array , the 13th simulated electrode allows a greater near proximity

detection distance and an increased sensing area.

Features

• 1.71V to 3.6V operation

• 29 μA typical run current at 16 ms sampling interval

•3 μA in scan stop mode current

• 12 electrodes/capacitance sensing inputs in which 8 are

multifunctional for LED driving and GPIO

• Integrated independent autocalibration for each ele ctrod e input

• Autoconfiguration of charge current and charge time for each

electrode input

• Separate touch and release trip thresholds for each electrode,

providing hysteresis and electrode independ ence

•I

2C interface, with IRQ Interrupt output to advise electrode status

changes

• 3 mm x 3 mm x 0.65 mm 20 lead QFN package

• -40°C to +85°C operating temperature range

Implementations

• General Purpose Capacitance Detection

• Switch Replacements

• Touch Pads, Touch Wheel, Touch Slide Bar, Touch Screen Panel

• Capacitance Near Proximity Detection

Typical Applications

• PC Peripherals

• MP3 Players

• Remote Controls

• Mobile Phones

• Lighting Controls

ORDERING INFORMATION

Device Name Temperature Range Case Number Touch Pads I2C Address Shipping

MPR121QR2 -40°C to +85°C 2059 (20-Pin QFN) 12-pads 0x5A - 0x5D Tape & Reel

MPR121

Top View

Pin Connections

Bottom View

20-PIN QFN

CASE 2059-01

678910

1617181920

ELE4

ELE3

ELE6

ELE7

ELE5

VSS

REXT

ELE0

ELE1

ADDR

VREG

SCL

IRQ

SDA

ELE2

VDD

ELE11

ELE10

ELE9

ELE8

MPR121

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1 Pin Descriptions

Table 1. Pin Descriptions

Pin No.

Pin Name Description

1 IRQ Open Collector Interrupt Output Pin, active low

2SCL I2C Clock

3SDA I2C Data

4ADDR I2C Address Select Input Pin. Connect the ADDR pin to the VSS, VDD, SDA or SCL line, the resulting I2C addresses

are 0x5A, 0x5B, 0x5C and 0x5D respectively

5 VREG Internal Regulator Node – Connect a 0.1 μF bypass cap to VSS

6VSS Ground

7REXT External Resistor – Connect a 75 kΩ 1% resistor to VSS to set internal reference current

8ELE0 Electrode 0

9ELE1 Electrode 1

10 ELE2 Electrode 2

11 ELE3 Electrode 3

12 ELE4 Electrode 4

13 ELE5 Electrode 5

14 ELE6 Electrode 6

15 ELE7 Electrode 7

16 ELE8 Electrode 8

17 ELE9 Electrode 9

18 ELE10 Electrode 10

19 ELE11 Electrode 11

20 VDD Connect a 0.1 μF bypass cap to VSS

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2 Schematic Drawings and Imp l ementation

Figure 1. Power Configuration 1: MPR121 runs from a 1.71V to 2.75V supply.

Figure 2. Power Configuration 2: MPR121 runs from a 2.0V to 3.6V supply.

VDD

VDD ELE11/LED7

GND

0.1 μF

GND

1.71V to 2.75V

VSS

VREG

IRQ

SCL

SDA

ADDR

REXT

ELE10/LED6

ELE9/LED5

ELE8/LED4

ELE7/LED3

ELE6/LED2

ELE5/LED1

ELE4/LED0

ELE3

ELE2

ELE1

ELE0

MPR121Q

TOUCH SENSOR

75 kΩ 1%

VDD

VDD ELE11/LED7

GND

0.1 μF

75 kΩ 1%

2.0V to 3.6V

VSS

VREG

IRQ

SCL

SDA

ADDR

REXT

ELE10/LED6

ELE9/LED5

ELE8/LED4

ELE7/LED3

ELE6/LED2

ELE5/LED1

ELE4/LED0

ELE3

ELE2

ELE1

ELE0

MPR121Q

TOUCH SENSOR

GND GND

0.1 μF

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3 Device Operation Overview

Power Supply

The VDD pin is the main power supply input to the MPR121 and is always decoupled with a 0.1 μF ceramic capacitor to the VSS.

Excessive noise on the VDD should be avoided.

The VDD pin has an operational voltage range speci fication between 1.71V to 3.6V. The internal voltage regulator, which

generates current to internal circuitry, operates with an input range from 2.0V to 3.6V. To work with a powe r supply below 2.0V

and to avoid the unnecessary voltage drop, the internal voltage regulator can be bypassed, refer to Figure 1 and Figure 2.

When a power supply is in the range of 1.71V to 2.75V, the VDD and VREG pins can be connected together (Figure 1) so that

internal voltage regulator is bypassed. In this configuration, the supply voltage cannot be higher than 2.75V as this is the

maximum voltage limit for VREG pin.

When a power supply is higher than 2.75V , it must be connected to the VDD, i.e. configuration as in Figure 2. In this configuration,

a separate 0.1 μF decoupling ceramic capacitor on VREG to VSS is applied as a bypass cap for inte rna l circui try. This

configuration can work with a VDD supply voltage down to 2.0V. For a typical two dry cell 1.5V batteries application, this

configuration covers the entire expected working voltage range from 2.0V to 3.0V.

Capacitance Sensing

The MPR121 uses a constant DC current capacitance sensing scheme. It can measure capacitances ranging from 10 pF to over

2000 pF with a resolution up to 0.01 pF. The device does this by varying the amount of charge current and charge time applied

to the sensing inputs.

The 12 electrodes are controlled independently; this allows for a great deal of flexibility in electrode pattern design. An automatic

configuration system is integrated as part of the device, this greatly simplifies the individual register setup. Please refer to the

Freescale application note, AN 3889, for more details.

The voltage measured on the input sensing no de is inversely proportional to the capacitance. At the end of each charge circle,

this voltage is sampled by an internal 10-bit ADC. The sampled data is then processed through several stages of digital filtering.

The digital filtering process allows for good noise immunity in different environments. For more information on the filtering system,

refer to application note AN3890.

Touch Sensing

Once the electrode capacitance data is acquired, the electrode touch/release status is determined comparing it to the

capacitance baseline value. The capacitance baseline is tracked by MPR121 automati cally based on the background

capacitance variation.

The baseline value is compared with the current immediate electrode data to determine if a touch or release has occurred. A

designer has the ability to set the touch/release thresholds, as well as a touch/release debounce time. This is to eliminate jitter

and false touches due to noise. Additional informa tion on baseline capacitance system is covered in application notes AN3891

and AN3892.

Proximity Sensing

One new feature of the MPR121 is the near proximity sensing system. This means that all of the system’s electrodes can be

summed together to create a single large electrode. The major advantage of the large electrode is that is can cover a much larger

sensing area. The near proximity sensing system can be used while at the same time having separate electrodes by using touch

button sensing.

Proximity detection is read as an indepe ndent channel and has configuration registers similar to the other 12 channels. When

proximity detection is enabled, this “13th” measurement channel will be included at the beginning of a normal detection cycle.

This system is described in application note AN3893.

LED Driver

Among the 12 electrode inputs, 8 inputs are designed as multifunctional pins. When these pins are not configured as electrodes,

they may be used to drive LEDs or used for general purpose input or output. For more details on this feature, please refer to

application note AN3894.

Serial Communication

The MPR121 is an Inter-Integr ated Circuit (I 2C) compliant device with an interrupt IRQ pin. This pin is triggered any time a touch

or release is detected. T he device has a configurable I2C address by connecting the ADDR pin to the VSS, VDD, SDA or SCL

lines This results in I2C addresses of 0x5A, 0x5B, 0x5C and 0x5D. The specific details of this system are described in AN3895.

For reference, the register map of th e MPR121 is included in Table 2.

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Table 2. Register Map

Address Initial

Value

Auto-

Increment

Address

ELE0 - ELE7 Touch Status ELE7 ELE6 ELE5 ELE4 ELE3 ELE2 ELE1 ELE0 0x00 0x00

Address + 1

ELE8 - ELE11, ELEPROX Touch Status OVCF ELEPROX ELE11 ELE10 ELE9 ELE8 0x01 0x00

ELE0-7 OOR Status E7_OOR E6_OOR E5_OOR E4_OOR E3_OOR E2_OOR E1_OOR E0_OOR 0x02 0x00

ELE8-11, ELEPR OX OOR Statu s ACFF ARFF PROX_OOR E11_OOR E10_OOR E9_OOR E8_OOR 0x03 0x00

ELE0 Electrode Filtered Data LSB EFD0LB 0x04 0x00

ELE0 Electrode Filtered Data MSB EFD0HB 0x05 0x00

ELE1 Electrode Filtered Data LSB EFD1LB 0x06 0x00

ELE1 Electrode Filtered Data MSB EFD1HB 0x07 0x00

ELE2 Electrode Filtered Data LSB EFD2LB 0x08 0x00

ELE2 Electrode Filtered Data MSB EFD2HB 0x09 0x00

ELE3 Electrode Filtered Data LSB EFD3LB 0x0A 0x00

ELE3 Electrode Filtered Data MSB EFD3HB 0x0B 0x00

ELE4 Electrode Filtered Data LSB EFD4LB 0x0C 0x00

ELE4 Electrode Filtered Data MSB EFD4HB 0x0D 0x00

ELE5 Electrode Filtered Data LSB EFD5LB 0x0E 0x00

ELE5 Electrode Filtered Data MSB EFD5HB 0x0F 0x00

ELE6 Electrode Filtered Data LSB EFD6LB 0x10 0x00

ELE6 Electrode Filtered Data MSB EFD6HB 0x11 0x00

ELE7 Electrode Filtered Data LSB EFD7LB 0x12 0x00

ELE7 Electrode Filtered Data MSB EFD7HB 0x13 0x00

ELE8 Electrode Filtered Data LSB EFD8LB 0x14 0x00

ELE8 Electrode Filtered Data MSB EFD8HB 0x15 0x00

ELE9 Electrode Filtered Data LSB EFD9LB 0x16 0x00

ELE9 Electrode Filtered Data MSB EFD9HB 0x17 0x00

ELE10 Electrode Filtered Data LSB EFD10LB 0x18 0x00

ELE10 Electrode Filtered Data MSB EFD10HB 0x19 0x00

ELE11 Electrode Filtered Data LSB EFD11LB 0x1A 0x00

ELE11 Electrode Filtered Data MSB EFD11HB 0x1B 0x00

ELEPROX Electrode Filtered Data LSB EFDPROXLB 0x1C 0x00

ELEPROX Electrode Filtered Data MSB EFDPROXHB 0x1D 0x00

ELE0 Baseline Value E0BV 0x1E 0x00

ELE1 Baseline Value E1BV 0x1F 0x00

ELE2 Baseline Value E2BV 0x20 0x00

ELE3 Baseline Value E3BV 0x21 0x00

ELE4 Baseline Value E4BV 0x22 0x00

ELE5 Baseline Value E5BV 0x23 0x00

ELE6 Baseline Value E6BV 0x24 0x00

ELE7 Baseline Value E7BV 0x25 0x00

ELE8 Baseline Value E8BV 0x26 0x00

ELE9 Baseline Value E9BV 0x27 0x00

ELE10 Baseline Value E10BV 0x28 0x00

ELE11 Baseline Value E11BV 0x29 0x00

ELEPROX Baseline Value EPROXBV 0x2A 0x00

MHD Rising MHDR 0x2B 0x00

NHD Amount Rising NHDR 0x2C 0x00

NCL Rising NCLR 0x2D 0x00

FDL Rising FDLR 0x2E 0x00

MHD Falling MHDF 0x2F 0x00

NHD Amount Falling NHDF 0x30 0x00

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NCL Falling NCLF 0x31 0x00

Address + 1

FDL Falling FDLF 0x32 0x00

NHD Amount Touched NHDT 0x33 0x00

NCL Touched NCLT 0x34 0x00

FDL Touched FDLT 0x35 0x00

ELEPROX MHD Rising MHDPROXR 0x36 0x00

ELEPROX NHD Amou nt Rising NHDPROXR 0x37 0x00

ELEPROX NCL Rising NCLPROXR 0x38 0x00

ELEPROX FDL Rising FDLPROXR 0x39 0x00

ELEPROX MHD Falling MHDPROXF 0x3A 0x00

ELEPROX NHD Amou nt Falling NHDPROXF 0x3B 0x00

ELEPROX NCL Falling NCLPROXF 0x3C 0x00

ELEPROX FDL Falling FDLPROXF 0x3D 0x00

ELEPROX N HD Amount Touched NHDPROXT 0x3E 0x00

ELEPROX NCL Touched NCLPROXT 0x3F 0x00

ELEPROX FDL Touched FDLPROXT 0x40 0x00

ELE0 Touch Threshold E0TTH 0x41 0x00

ELE0 Release Threshold E0RTH 0x42 0x00

ELE1 Touch Threshold E1TTH 0x43 0x00

ELE1 Release Threshold E1RTH 0x44 0x00

ELE2 Touch Threshold E2TTH 0x45 0x00

ELE2 Release Threshold E2RTH 0x46 0x00

ELE3 Touch Threshold E3TTH 0x47 0x00

ELE3 Release Threshold E3RTH 0x48 0x00

ELE4 Touch Threshold E4TTH 0x49 0x00

ELE4 Release Threshold E4RTH 0x4A 0x00

ELE5 Touch Threshold E5TTH 0x4B 0x00

ELE5 Release Threshold E5RTH 0x4C 0x00

ELE6 Touch Threshold E6TTH 0x4D 0x00

ELE6 Release Threshold E6RTH 0x4E 0x00

ELE7 Touch Threshold E7TTH 0x4F 0x00

ELE7 Release Threshold E7RTH 0x50 0x00

ELE8 Touch Threshold E8TTH 0x51 0x00

ELE8 Release Threshold E8RTH 0x52 0x00

ELE9 Touch Threshold E9TTH 0x53 0x00

ELE9 Release Threshold E9RTH 0x54 0x00

ELE10 Touch Threshold E10TTH 0x55 0x00

ELE10 Release Thresho l d E10RTH 0x56 0x00

ELE11 Touch Threshold E11TTH 0x57 0x00

ELE11 Release Thresho l d E11RTH 0x58 0x00

ELEPROX Touch Threshold EPROXTTH 0x59 0x00

ELEPROX Relea s e Thre sho ld EPROXRTH 0x5A 0x00

Debounce Touch & Release DR DT 0x5B 0x00

Filter/Global CDC Co nfiguration FFI CDC 0x5C 0x10

Filter/Global CDT Configuration CDT SFI ESI 0x5D 0x24

Electrode Config ur ation CL ELEPROX_EN ELE_EN 0x5E 0x00

ELE0 Electrode Current CDC0 0x5F 0x00

ELE1 Electrode Current CDC1 0x60 0x00

ELE2 Electrode Current CDC2 0x61 0x00

Table 2. Register Map

Address Initial

Value

Auto-

Increment

Address

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ELE3 Electrode Current CDC3 0x62 0x00

Address + 1

ELE4 Electrode Current CDC4 0x63 0x00

ELE5 Electrode Current CDC5 0x64 0x00

ELE6 Electrode Current CDC6 0x65 0x00

ELE7 Electrode Current CDC7 0x66 0x00

ELE8 Electrode Current CDC8 0x67 0x00

ELE9 Electrode Current CDC9 0x68 0x00

ELE10 Electrode Current CDC10 0x69 0x00

ELE11 Electrode Current CDC11 0x6A 0x00

ELEPROX Electrode Current CDCPROX 0x6B 0x00

ELE0, ELE1 Charge Time CDT1 CDT0 0x6C 0x00

ELE2, ELE3 Charge Time CDT3 CDT2 0x6D 0x00

ELE4, ELE5 Charge Time CDT5 CDT4 0x6E 0x00

ELE6, ELE7 Charge Time CDT7 CDT6 0x6F 0x00

ELE8, ELE9 Charge Time CDT9 CDT8 0x70 0x00

ELE10, ELE11 Charge Time CDT11 CDT10 0x71 0x00

ELEPROX Charge Time CDTPROX 0x72 0x00

GPIO Control Register 0 CTL011 CTL010 CTL09 CTL08 CTL07 CTL06 CTL05 CTL04 0x73 0x00

GPIO Control Register 1 CTL111 CTL110 CTL19 CTL18 CTL17 CTL16 CTL15 CTL14 0x74 0x00

GPIO Data Register DAT11 DAT10 DAT9 DAT8 DAT7 DAT6 DAT5 DAT4 30x75 0x00

GPIO Direction Register DIR11 DIR10 DIR9 DIR8 DIR7 DIR6 DIR5 DIR4 0x76 0x00

GPIO Enable Register EN11 EN10 EN9 EN8 EN7 EN6 EN5 EN4 0x77 0x00

GPIO Data Set Register SET11 SET10 SET9 SET8 SET7 SET6 SET5 SET4 0x78 0x00

GPIO Data Clear Register CLR11 CLR10 CLR9 CLR8 CLR7 CLR6 CLR5 CLR4 0x79 0x00

GPIO Data Toggle Register TOG11 TOG10 TOG9 TOG8 TOG7 TOG6 TOG5 TOG4 0x7A 0x00

AUTO-CONFIG Control Register 0 FFI RETRY BVA ARE ACE 0x7B 0x00

AUTO-CONFIG Control Register 1 SCTS OORIE ARFIE ACFIE 0x7C 0x00

AUTO-CONFIG USL Register USL 0x7D 0x00

AUTO-CONFIG LSL Register LSL 0x7E 0x00

AUTO-CONFIG Target Level Register TL 0x7F 0x00 0x00

Soft Reset Register SRST 0x80

Table 2. Register Map

Address Initial

Value

Auto-

Increment

Address

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4 Electrical Characteristics

4.1 Absolute Maximum Ratings

Absolute maximum ratings are stress ratings only and functional operation at the maxima is not guaranteed. S tress beyond the

limits specified in Table 3 may affect device reliability or cause permanent damage to the device. For functional operating

conditions, refer to the remaining tables in this section. This device contains circuitry protecting against damage due to high-static

voltage or electrical fields; however, it is advised that normal precautions be taken to avoid application of any voltages higher

than maximum-rated voltages to this high-impedance circuit.

4.2 ESD and Latch-up Protection Characteristics

Normal handling precautions should be used to avoid exposur e to static discharge.

Qualification tests are performed to ensure that these device s can withstand exposure to reasonable levels of static without

suffering any permanent damage. During the device qualification, ESD stresses were performed for the Human Body Model

(HBM), the Machine Model (MM) and the Charge Device Model (CDM).

A device is defined as a failure if after exposure to ESD pulses, the device no longer meets the device specification. Complete

DC parametric and functional testing is performed per the applicable device specification at room temperature followed by hot

temperature, unless specified otherwise in th e device specification.

Table 3. Absolute Maximum Ratings - Voltage (with respect to VSS)

Rating Symbol Value Unit

Supply Voltage VDD -0.3 to +3.6 V

Supply Voltage VREG -0.3 to +2.75 V

Input Voltage

SCL, SDA, IRQ VIN VSS - 0.3 to VDD + 0.3 V

Operating Temperature Range TO-40 to +85 °C

GPIO Source Current per Pin iGPIO 12 mA

GPIO Sink Current per Pin iGPIO 1.2 mA

Storage Temperature Range TS-40 to +125 °C

Table 4. ESD and Latch-up Test Conditions

Rating Symbol Value Unit

Human Body Model (HBM) VESD ±2000 V

Machine Model (MM) VESD ±200 V

Charge Device Model (CDM) VESD ±500 V

Latch-up current at TA = 85°C ILATCH ±100 mA

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4.3 DC Characteristics

This section includes information abo ut power supply requirements and I/O pin characteristics.

4.4 AC Characteristics

Table 5. DC Characteristics

(Typical Operating Circuit, VDD and VREG = 1.8V, TA = 25°C, unless otherwise noted.)

Parameter Symbol Conditions Min Typ Max Units

High Supply Voltage VDD 2.0 3.3 3.6 V

Low Supply Voltage VREG 1.71 1.8 2.75 V

Average Supply Current(1)

1.: ECR set to 0x2C and all 12 channels plus one proximity channel activated. Measurement current CDC is set at maximum of 0x3F.

IDD

Run Mode @ 1 ms sample period 393 μA

Run Mode @ 2 ms sample period 199 μA

Run Mode @ 4 ms sample period 102 μA

Run Mode @ 8 ms sample period 54 μA

Run Mode @ 16 ms sample period 29 μA

Run Mode @ 32 ms sample period 17 μA

Run Mode @ 64 ms sample period 11 μA

Run Mode @ 128 ms sample period 8 μA

Measurement Supply Current IDD Peak of measurement duty cycle 1 mA

Idle Supply Current IDD Stop Mode 3 μA

Input Leakage Current ELE_ IIH, IIL 0.025 μA

Input Self-Capacitance on ELE_ 15 pF

Input High Voltage SDA, SCL VIH 0.7 x VDD V

Input Low Voltage SDA, SCL VIL 0.3 x VDD V

Input Leakage Current

SDA, SCL IIH, IIL 0.025 1 μA

Input Capacitance

SDA, SCL 7pF

Output Low Voltage

SDA, IRQ VOL IOL = 6mA 0.5V V

Output High Voltage

ELE4 - ELE11 (GPIO mode) VOHGPIO

VDD = 2.7V to 3.6V: IOHGPIO = -10 mA

VDD = 2.3V to 2.7V: IOHGPIO = -6 mA

VDD = 1.8V to 2.3V: IOHGPIO = -3 mA VDD - 0.5 V

Output Low Voltage

ELE4 - ELE11 (GPIO mode) VOLGPIO IOLGPIOD = 1 mA 0.5 V

Power On Reset VTLH VDD rising 1.08 1.35 1.62 V

VTHL VDD falling 0.88 1.15 1.42 V

Table 6. AC Characteristics

(Typical Operating Circuit, VDD and VREG = 1.8V, TA = 25°C, unless otherwise noted.)

Parameter Symbol Conditions Min Typ Max Units

8 MHz Internal Oscillator fH7.44 8 8.56 MHz

1 kHz Internal Oscillator fL0.65 1 1.35 kHz

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4.5 I2C AC Characteristics

Table 7. I2C AC Characteristics

(Typical Operating Circuit, VDD and VREG = 1.8V, TA = 25°C, unless otherwise noted.)

Parameter Symbol Conditions Min Typ Max Units

Serial Clock Frequency fSCL 400 kHz

Bus Free Time Between a STOP and a START Condition tBUF 1.3 μs

Hold Time, (Repeated) START Condition tHD, STA 0.6 μs

Repeated START Condition Setup Time tSU, STA 0.6 μs

STOP Condition Setup Time tSU, STO 0.6 μs

Data Hold Time tHD, DAT 0.9 μs

Data Setup Time tSU, DAT 100 ns

SCL Clock Low Period tLOW 1.3 μs

SCL Clock High Period tHIGH 0.7 μs

Rise Time of Both SDA and SCL Signals, Receiving tR20+0.1Cb300 ns

Fall Time of Both SDA and SCL Signals, Receiving tF20+0.1Cb300 ns

Fall Time of SDA Transmitting tF.TX 20+0.1Cb250 ns

Pulse Width of Spike Suppressed tSP 25 ns

Capacitive Load for Each Bus Line Cb400 pF

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5 Register Operation Descriptions

5.1 Register Read/Write Operations and Measurement Run/Stop Mode

After power on reset (POR) or soft reset by command, all registers are in reset default initial value (see Table 2). All the registers,

except registers 0x5C (default 0x10) and 0x5D (default 0x24), are clea red.

Registers 0x2B ~ 0x7F are control and configuration registers which need to be correctly configured before any capacitance

measurement and touch detection.

Registers 0x00 ~ 0x2A are output registers updating periodically by the MPR121 in Run Mode. Amo ng these output registers,

Baseline V alue Registers 0x1D ~ 0x2A are also writable, this is sometimes useful when user specific baseline values are desired.

The MPR121’s Run Mode and Stop Mode are controlled by control bits in Electrode Configuration Register (ECR, 0x5E). When

all ELEPROX_EN and ELE_EN bits are zeros, the MPR121 is in Stop Mode. While in Stop Mode, there are no capacitance or

touch detection measurement on any of the 13 channels. When any of the ELEPROX_EN and ELE_EN bits are set to ‘1’, the

MPR121 is in Run Mode. The MPR121 will continue to run on its own until it is set again to Stop Mode by the user.

The MPR121 registers read operation can be done at any time, either in Run Mode or in S top Mode. However , the register write

operation can only be done in Stop Mode. The ECR (0x5E) and GPIO/LED control registers (0x73~0x7A) can be written at

anytime.

5.2 Touch Status Registers (0x00~0x01)

These two registers indicate the detected touch/release status of all of the 13 sensing input channels. ELEPROX is the status for

the 13th proximity detection channel. The update rate of these status bits will be {ESI x SFI}.

ELEx, ELEPROX: Touch or Release status bit of each respective channel (read only).

1, the respective channel is currently deemed as touched.

0, the respective channel is deemed as released.

Note: When an input is not configured as an electrode and enabled as GPIO input port, the corresponding status bit shows the

input level, but these GPIO status changes will not cause any IRQ interrupt. This feature is for ELE4~ELE11 only.

OVCF: Over Current Flag (read and write)

1, over current was detected on REXT pin.

0, normal condition.

When over current is detected, the OVCF is set to ‘1’ and the MPR121 goes to Stop Mode. All other bits in status registers

0x00~0x03, output registers 0x04~0x2A, and bits D5~D0 in ECR (0x5E) will also be cleared. When the bit is set at ‘1’, the write

to the ECR register to enter Run Mode will be discarded. The write to ’1’of the OVCF will clear this bit and the MPR121 fault

condition will be cleared. The MPR121 can then be configured to return to the Run Mode again.

ELE0-ELE7 Touch Status (0x00)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read ELE7 ELE6 ELE5 ELE4 ELE3 ELE4 ELE1 ELE0

Write — — — — — — — —

ELE8-ELE11 ELEPROX Touch Status (0x01)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read OVCF — — ELEPROX ELE11 ELE10 ELE9 ELE8

Write — — — — — — — —

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5.3 Electrode Filtered Dat a Register (0x04~0x1D)

The MPR121 provides filtered electrode output data for al l 13 channels. The output data is 10-bit and comes from the internal

2nd stage filter output. The data range is 0~1024 or 0x000~0x400 in Hex. Bit 0~7 of the 10-bit data are stored in the low byte and

bit 9 and bit 8 are stored in the high byte. The data is the measured voltage on each channel and inversely proportio nal to the

capacitance on that channel.

These registers are read only and are updat ed every {ESI x SFI}. A multibyte read operation to read both LSB and MSB is

recommended to keep the data coherency (i.e, LSB and MSB matching). A multibyte reading of 0x00~0x2A returns results of a

single moment without mixing up old and new data.

5.4 Baseline Value Register (0x1E~0x2A)

Along with the 10-bit electrode filtered data output, each channel also has a 10-bit baseline value. The update rate of these

registers is {ESI x SFI} if baseline tracking operation is enabled. These values are the output of the internal baseline filter

operation tracking the slow-voltage variation of the background capacitance change. Touch/release detection is made based on

the comparison between the 10-bit electrode filtered data and the 10-bit baseline value.

Note: Although internally the baseline value is 10-bit, users can only access the 8 MSB of the 10-bit baseline value through the

baseline value registers. The read out from the baseline register must be left shift two bits before comparing it with the 10-bit

electrode data.

The Baseline Value register is writable in Stop Mode. Note: when the user writes into the baseline value register, the lower two

bits of the 10-bit baseline value are automatically cleared inte rnally upon write operation. The Write to Baseline Value Register

by specific values can be sometimes useful if user wants to manipulate the touch/release status. For example, manually setting

the target channel from a touch locked state into a touch released state is easily done by setting the baseline value above the

signal data.

Refer to the Electrode Configuration Register (ECR, 0x5E) on how to control the on/off operation of baseline tracking and further

details on how the initial baseline data is loaded into Run Mode. Refer to Baseline Filtering Control registers(0x2B~0x2A) on how

to control the filtering of the baseline value.

5.5 Baseline Filtering Control Register (0x2B~0x40)

All12 of the electrode baseline values are controlled by the same set of filtering control registers, 0x2B ~ 0x35. The 13th channel

ELEPROX is controlled by registers 0x36 ~ 0x40. Both sets of registers have the same structure using three different scenarios;

rising, falling, and touched.

Rising is defined as when the electrode data is greater than the baseline value. Falling is defined as when the electrode data is

less than the baseline value. Touched is when the electrode is in touched status. For each scenario, the filtering characteristic is

further defined by four parameters: the maximum half delta (MHD), noise half delta (NHD), noise count limit (NCL) and filter delay

count limit (FDL). Note: there is no maximum half delta for the touched scenario.

Maximum Half Delta (MHD): Determines the largest magnitude of variation to pass through the baseline filter . The range of the

effective value is 1~63.

Noise Half Delta (NHD): Determines the incremental change when non-noise drift is detected. The range of the effective value

is 1~63.

Electrode Filtered Data Low Byte (0x04,0x06,...,0x1C)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

Write — — — — — — — —

Electrode Filtered Data High Byte (0x05,0x07,...,0x1D)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read — — — — — — Bit 9 Bit 8

Write — — — — — — — —

Electrode Baseline Value (0x1E~0x2A)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2

Write

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Noise Count Limit (NCL): Determines the number of samples consecutivel y greater than the Max Half Delta value. This is

necessary to determine th at it is not noise. The range of the effective value is 0~255.

Filter Delay Count Limit (FDL): Determines the operation rate of the filter . A larger count limit means the filter delay is operating

more slowly. The range of the effective value is 0~255.

The setting of the filter is depended on the actual applicati on. For more information on these registers, refer to appli c ation note

AN3891.

5.6 Touch / Release Threshold (0x41~0x5A)

ExTTH: Electrode touch threshold , in range of 0~0xFF.

ExRTH: Electrode release threshold, in range of 0~0xFF.

Each of the 13 channels can be set with its own set of touch and release thresholds. Touch and release are dete cted by

comparing the electrode filtered data to the baseline value. The amount of deviation from the baseline value represents a

immediate capacitance change detected by possible a touch/relea s e action.

Touch condition: Baselin e - Electrode filtere d data > Touch threshold

Release condition: Baseline - Electrode filtered data < Release threshold

Threshold settings are dependant on th e touch/release signal strength, system sensitivity and noise immunity requirements. In

a typical touch detection application, threshold is typically in the range 0x04~0x10. The touch threshold is several counts larger

than the release threshold. This is to provide hysteresis and to prevent noise and jitter. For more information, refer to the

application note AN3892 and the MPR121 design guidelines.

5.7 Debounce Register (0x5B)

DT: Debounce number for touch. The value range is 0~7.

DR: Debounce number for release. The value range is 0~ 7.

All 13 channels use the same set of touch and release debounce numbers. The status bits in S t atus Register 0x00 and 0x01 will

only take place after the number of consecutive touch or release detection meets the debounce number setting. The debounce

setting can be very useful in avoiding possible noise glitches. Using the debounce setting, the status bit change will have a delay

of {ESI x SFI x DR (or DT)}.

ELEx, ELEProx Touch Threshold (0x41,0x43,...,0x59)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read ExTTH

Write

ELEx, ELEProx Release Threshold (0x42,0x44,...,0x5A)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read ExRTH

Write

Debounce Register (0x5B)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read —DR —DT

Write

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5.8 Filter and Global CDC CDT Configuration (0x5C, 0x5D)

Filter/Global CDC Configu ration Reg ister (0x5C)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read FFI CDC

Write

Filter/Global CDT Configuration Register (0x5D)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read CDT SFI ESI

Write

Table 8. Bit Descriptions

Field Description

FFI

First Filter Iterations - The first filter iterations field selects the number of samples taken as

input to the first level of filtering.

00 Encoding 0 - Sets samples taken to 6 (Default)

01 Encoding 1 - Sets samples taken to 10

10 Encoding 2 - Sets samples taken to 18

11 Encoding 3 - Sets samples taken to 34

CDC

Charge Discharge Current - Selects the global value of charge discharge current applied to

electrode. The maximum is 63 μA, 1 μA step.

000000 Encoding 0 - Disable Electrode Charging

000001 Encoding 1 - Sets the current to 1 μA

010000 Encoding 16 - Sets the current to 16 μA (Default)

111111 Encoding 63 - Sets the current to 63 μA

CDT

Charge Discharge Time - Selects the global value of charge time applied to electrode.

The maximum is 32 μs, programmable as 2 ^(n-2) μs.

000 Encoding 0 - Disables Electrode Charging

001 Encoding 1 - Time is set to 0.5 μs (Default)

010 Encoding 2 - Time is set to 1 μs

111 Encoding 7 - Time is set to 32 μs

SFI

Second Filter Iterations - Selects the number of samples taken for the second level filter

00 Encoding 0 - Number of samples is set to 4 (Default)

01 Encoding 1 - Number of samples is set to 6

10 Encoding 2 - Number of samples is set to 10

11 Encoding 3 - Number of samples is set to 18

ESI

Electrode Sample Interval - Selects the period between samples used for the second level

of filtering. The maximum is 128ms, Programmable to 2^n ms

000 Encoding 0 - Period set to 1 ms

001 Encoding 1 - Period set to 2 ms

100 Encoding 4 - Period set to 16 ms (Default)

111 Encoding 7 - Period set to 128 ms

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These two registers set the global AFE settin gs. This includes global electrode charge/discharge current CDC, global charge/

discharge time CDT, as well as a common filtering setting (FFI, SFI, ESI) for all 13 channels, including the 13th Eleprox channel.

The register 0x5C holds the global CDC and the first level filter configuration for all 13 channels. For each enabled channel, the

global CDC will be used for that channel if the respective charge discharge current CDCx setting in 0x5F~0x6B for that channel

is zero. If it is not zero, the individual CDCx value will be used in place of the global CDC value. If the MPR121’s auto-configuration

feature is enabled, CDCx will be automatically set up during system start stage and used for the actual measurement.

The register 0x5D holds the global CDT and the second level filter configuration for all 13 channels. For each enabled channel,

the global CDT will be used for that channel if the respective charge discharge time CDTx setting in 0x6C~0x72 for that channel

is zero. If it is not zero, the individual CDTx value will be used in place of the global CDT value. If the SCTS bit (Skip Charge T ime

Search) in the MPR121’s autoconfiguration is set, then the current global CDT and CDTx will be used for each channel

measurements. If not, then the individual CDTx will be automatically set up during the system start stage and used for the actual

measurement.

Using only the global CDC and/or global CDT is acceptable where the capacitance values from all 13 channels are similar . If the

electrode pattern, size, or even overlay and base material type changes from one channel to another , then using individual CDCx

(and CDTx) will have a better result on sensing sensitivity as each electrode is charged up to a point closing to the supply voltage

rail so that the highest sensing field is built for each channel.

The settings for the FFI, SFI, and ESI must be selected according to the system design noise filtering requirement. These settings

must also balance the need for power consumption and response time.

When the total time required by scanning and charging/discharge all the enabled channels is longer than the ESI setting, then

the actual time will override the ESI setting. For exam pl e if the ESI = 4 (16 mS), when FFI = 3 (34 samples), CDT = 7 (32 μS),

with all 13 channels enabled, the scan time needed is 34 x (32 μS + 32 μS) x 13 = 28 mS. This 28 mS will be the actual sampling

interval instead of ESI (16 mS).

5.9 Electrode Charge Current Register (0x5F~0x6B)

CDCx: Sets the charge current applied to each channel. Similar to global CDC value, the range is 0~63 μA, from 0x00~0x3F in

1 μA step. When the CDCx is zero, the global CDC value will be used for that channel.

The individual CDCx bit can either be set manually or automatically (if autoconfiguration is enabled). When the autoconfiguration

is enabled, during the first transition from Stop Mode to Run Mode, the system will automatically run a trial search for the

appropriate CDCx (and CDTx if SCTS = 0). The individual CDCx will be automatically updated by the MPR121 into the respective

registers once autoconfiguration is finished. CDCx is used in the following capacitance measurement and touch detection.

5.10 Electrode Charge Time Register (0x6C~0x72)

CDTx: Sets the charge time applied to each channel. Similar to the global CDT value, the range is 0~32 μS, from 2b000~2b111.

When the CDTx is zero, the global CDT value is used for that channel.

The individual CDTx bit can be set manually or automatically (if autoconfiguration is enabled). When autoconfiguration is enabled,

during the first transition from S top Mode to Run Mode, the system will automatically run a trial search for the appropriate CDCx

(and CDTx if SCST = 0). This means the autoconfiguration will include a search on the CDTx. The individua l CDTx will be

automatically updated by the MPR121 into the respective registers once the autoconfiguration is finished. This data is used in

the following capacitance measurement and touch detection. If SCTS bit is 1, the search on CDTx will be skipped.

Electrode Charge Current (0x5F~0x6B)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read — — CDCx

Write — —

Electrode Charge Time (0x6C~0x72)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read —CDTx+1 —CDTx

Write — —

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5.11 Electrode Configuration Register (ECR, 0x5E)

The Electrode Configuration Register (ECR) determines if the MPR121 is in Run Mode or Stop Mode, controls the baseline

tracking operation and specifies the input confi gurations of the 13 channels.

The ECR reset default value is 0x00, which means MPR121 is in Stop Mode without capacitance measurement on all

13 channels. Setting ELEPROX_EN and/or ELE_EN control bits to non-zero data will put the MPR121 into Run Mode. This will

cause the MPR121 to operate immediately on its own. Clearing the ELEPROX_EN and ELE_EN all to zeros will set the MPR121

into Stop Mode (which is its lowest power state). The MPR121 can be switched between Stop Mode and Run Mode at anytime

by configuring the ECR.

If all channels including the13th proximity detection channel are enabled, the proximity sensing channel is scanned first, followed

by ELE0, ELE1..., and ELE1 1 respectively. The scan runs periodically at the sampling rate specified by the ESI in the Filter/CDT

Configuration Register (0x5D). Refer to the table above for configuration of the different channels. Enabling specific channels will

save the scan time and sensing field power spent on the unu sed channels.

In a typical touch detection application, baseline tracking is enabled. This is to compensate for the environment and background

induced slow capacitance change to the input sensing channels. The CL bits can enable/disable the baseline tracking and specify

how to load the baseline initial values. Since the baseline tracking filtering system has a very large time constant and the initial

Electrode Configuration Register (0x5E)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read CL ELEPROX_EN ELE_EN

Write

Table 9. Bit Descriptions

Field Description

Calibration Lock - Controls the baseline tracking and how the baseline initial value is loaded

00 - Baseline tracking enabled, initial baseline value is current value in baseline value register

(Default)

01 - Baseline tracking is disabled

10 - Baseline tracking enabled, initial baseline value is loaded with the 5 high bits of the first

10-bit electrode data value

11 - Baseline tracking enabled, initial baseline value is loaded with all 10 bits of the first

electrode data value

ELEPROX_EN

Proximity Enable - Controls the operation of 13th Proximity Detection

00 - Proximity Detection is disabled (Default)

01 - Run Mode with ELE0~ELE1 combined for proximity detection enabled

10 - Run Mode with ELE0~ELE3 combined for proximity detection enabled

11 - Run Mode with ELE0~ELE11combined for proximity detection enabled

ELE_EN

Electrode Enable - Controls the operation of 12 electrodes detection

0000 - Electrode detection is disabled (Default)

0001 - Run Mode with ELE0 for electrode detection enabled

0010 - Run Mode with ELE0~ ELE1 for electrode detection enabled

0011 - Run Mode with ELE0~ ELE2 for electrode detection enabled

0100 - Run Mode with ELE0~ ELE3 for electrode detection enabled

0101 - Run Mode with ELE0~ ELE4 for electrode detection enabled

0110 - Run Mode with ELE0~ ELE5 for electrode detection enabled

0111 - Run Mode with ELE0~ ELE6 for electrode detection enabled

1000 - Run Mode with ELE0~ ELE7 for electrode detection enabled

1001 - Run Mode with ELE0~ ELE8 for electrode detection enabled

1010 - Run Mode with ELE0~ ELE9 for electrode detection enabled

1011 - Run Mode with ELE0~ ELE10 for electrode detection enabled

11xx - Run Mode with ELE0~ ELE11 for electrode detection enabled

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baseline value starts from zero, it will require a very long time for the baseline to ramp up. This results in a short period of no

response to touch after the MPR121 is first set to Run Mode. Setting the CL = 2b10 will command the MPR121 to load the initial

baseline value at the beginning of the Run Mode. This shortens the initial baseline ramp-up time so that user will not notice any

delay on touch detection. The MPR121 uses the five high bits of the first measured 10 bit electrode data.

Auto-Configuration Registers (0x7B~ 0x7F)

For each enabled channel, both the charge time and charge current must be set properly. This is so that a specified amount of

charge field can be built on the sensing pad and that the capacitance can be measured using the internal ADC. When all 13

channels are used, there are total 13 CDCx and 13 CDTx values which need to be configured.

The MPR121 provides an auto-configuration function which is able to automatically search and set the charging parameters.

When autoconfiguration is run, specific CDCx and CDTx combinations for the enabled channels can be obtained automatically.

This eliminates test trials on the prototype device and for further verification on final products. A key task for the design engineer

is to verify if the parameter settings generated by the MPR121 are acceptable. This verification ensures that the settings are

optimized each time MPR121 powers on and that the equipment can operate in many different environments.

The autoconfigura tion finds the optimized CDCx and CDTx combination for each channel so that the charge level

(I x T = V) on the each channel is as close as possible to the target setting specified by the designer. An upper and lower setting

limit are used to provide the boundaries necessary to verify if the system is setup to operate correctly. If the autoconfiguration

can not find the proper CDCx and CDTx value, an Out Of Range (OOR) status will be set for that channel.

Autoconfiguration operates each time the MPR121 transitions from Stop Mode to Run Mode. After autoconfiguration is

completed, a set of CDCx and CDTx values for each channel are calculated and automatically loaded into the corresponding

If autoconfiguration fails, the MPR121 has an au to-reconfiguration function. Autoreconfiguration runs at each sampling interval

if a channel has OOR status from a failed autoconfiguration. Autoreconfiguration will run until the OOR status is cleared or until

it is disabled.

There are five registers used to control the MPR121 auto-configuration feature. Registers 0x7B and 0x7C are used as the control

registers and registers 0x07D to 0x7F are used to hold the configuration target settings. Refer to application note AN3889 for

more information.

FFI: The FFI bits are the same as the FFI bits in register 0x5C for correct auto-configuration and reconfiguration operations.

ACE: Auto-Configuration Enable. 1: Enable, 0: Disable. When Enabled, the autoconfiguration will operate once at the beginning

of the transition from S top Mode to Run Mode. This includes search and update of the CDCx and CDTx for each enabled channel

(if SCTS = 0).

ARE: Auto-Reconfiguration Enable. 1: Enable, 0: Disable. When enabled, if the OOR is set for a channel after autoconfiguration,

autoreconfiguration will opera te on that channel on each sampling interval until the OOR is cleared.

BVA: Fill the BVA bits same as the CL bits in ECR (0x5E) register.

RETRY: Specifies the number of retries for autoconfiguration and autoreconfiguration if the configuration fails before setting

OOR.

Auto-Configure Control Register 0 (0x7B)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read FFI RETRY BVA ARE ACE

Write

Auto-Configure Control Register 1 (0x7C)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read SCTS — — — — OORIE ARFIE ACFIE

Write — — — —

00 - No retry

01 - retry 2 times

10 - retry 4 times

11 - retry 8 times

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SCTS: Skip Charge Time Search.

1: Skip CDTx search and update when autoconfiguration or autoreconfiguration, and current global CDT or CDTx are used

for respective channels. CDT or CDTx needs to be specified by the designer manually before operation. Setting the SCTS

to “1” results in a shorter time to complete autoconfiguration. This is useful for when the designer has obtained the correct

CDTx / CDT, and is confident that the current CDT and CDTx settings work in all conditions.

0: Both CDTx and CDCx will be searched and set by autoconfiguration and/or autoreconfiguration.

ACFIE: Auto-configuration fail inte rrupt enable. 1: Enable, 0: Disable

ARFIE: Auto-reconfiguration fail interrupt enable. 1: Enable, 0: Disable

OORIE: Out-of-range interrupt enable . 1: Enable, 0: Disable

USL: Up-Side Limit. This value sets the electrode data level up limit for the boundary check in autoconfiguration and

autoreconfiguration operation.

LSL: Low-Side Limit. This value sets the electrode data level low limi t fo r the bound ary check in autoconfiguration an d

autoreconfiguration opera tion.

TL: Target Level. This value is the expected target electrode data level for autoconfiguration and autoreconfiguration, that is, after

successful autoconfiguration and autoreconfigu ration, the measured electrode data level when untouched shall be close to the

TL value. TL shall be in between of USL and LSL.

The three parameters, USL, LSL and TL, are in the format similar to the baseline value; only the eight high bits are accessible

by user and the two low bits are set to zero automatically . The USL/LSL/TL data needs to be shifted lef t two bits before comparing

with the electrode data or the 10-bit baseline value.

In order to have a valid auto-configuration result, USL/LSL/TL values should follow the relation that 255 > USL > TL > LSL > 0.

For example, USL = 200, TL = USL*0.9 = 180, LSL = USL*0.5 = 100.

It is possible that in a end user environment, the channel differences may be significant. This is because the same set of USL/

LS/TL data is being used for all channels. It is important that the parameters not be set too close together . This makes it difficult

for the autoconfiguration to find a suitable charge setting for a specific channe l. In this case, the electrode data might easi ly go

out of USL and LSL setting limits. Since the data is out-of-range, the channel status becomes OOR. If the channel is still OOR

after the autoconfiguration has been run, it may indicate that th e settings for this channel have not yet been optimized. One

solution to this problem is to manually review the USL/LSL/TL settings. Another possible reason why the channel status could

be OOR is a problem with the channel itself. This could be caused by a short to ground, short to the power rail, or short to the

pad of the other channel.

For the TL setting, a good practice is to try to set it close to the USL. This so the charge field can be set to detect a weak touch.

On the other hand, the TL should not be set too close to the USL so that it is constantly exceeding the limit. For example, the

electrode data from the end user’s environment might have a much wider variance of readings. Some of the readings might

exceed the USL, causing the auto-configuration to fail. For this reason, if the amount of capacitance change in the end user

environment is significant, it is suggested that the USL and TL be set low enough to give some headroom for possible capacitance

variations.

Up-Side Limit Register (0x7D)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read USL

Write

Low-Side Limit Register (0x7E)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read LSL

Write

Target Level Register (0x7F)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read TL

Write

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With above mentioned, one possible example setting is given out below using equation 1~3, with the assumption that setting TL

at 90% of USL, and LSL at 65% of USL would cover most of the application case. It may need further adjustment in some cases

but will be a very good start.

USL = (VDD - 0.7)/VDD x 256 Eqn. 1

TL = USL x 0.9 = (VDD - 0.7)/VDD x 256 x 0.9 Eqn. 2

LSL = USL x 0.65 = (VDD-0.7) / VDD x 256 x 0.65 Eqn. 3

Cin = I x T / V = CDC x CDT / (ADC counts x VDD/1024) Eqn. 4

It may not necessary to set the USL at the level of VDD - 0.7 but it is beneficial to keep the applied constant charge current as

accurate as that specified in the data sheet. This so the ca pacitance value on the input can be calculated with high accuracy

using ADC conversion Equation 4. Using VDD-0.7 as USL level allows some headroom for applications where the supply varies

over a certain range. For a system where the supply changes over a range, the lowest VDD point is considered for

autoconfiguration so that a relative lower charge field can be used to avoid clipping the electrode data to VDD when it drops.

5.12 Out-Of-Range Status Registers (0x02, 0x03)

Ex_OOR, EPROX_OOR: Out-Of-Range Status bit s for the 13 channels. This bit set indicates that a corresponding channel has

failed autoconfiguration and autoreconfiguration for range check. Those bits are cleared when they pass the auto-configuration

and auto-reconfiguration range check. These bits are user read only.

ACFF: Auto-Configuration Fail Flag. When autoconfiguration fails, this bit is set. This bit is user read only.

ARFF: Auto-Reconfiguration Fail Flag. When autoreconfiguration fails, this is bit set. This bit is user read only.

When autoconfiguration and/or autoreconfiguration are enabled, MPR121 checks the electrode data after each auto-

configuration, auto-reconfiguration operation to see if it is still in the range set by USL and LSL. When electrode data goes out of

the range, corresponding Ex_OORx bit becomes “1” to indicate the failed channels. One example of triggering OOR error is

shorting the me asurement sensing pad to power rails, or shorting it with other channels.

5.13 Soft Rest Register (0x80)

Write 0x80 with 0x63 asserts soft reset. The soft reset does not effect the I2C module, but all others reset the same as POR.

5.14 GPIO Registers (0x73~0x7A)

ELE0~ELE7 OOR Status (0x02)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read E7_OOR E6_OOR E5_OOR E4_OOR E3_OOR E2_OOR E1_OOR E0_OOR

Write — — — — — — — —

ELE8~ELEPROX OOR Status (0x03)

Bit D7 D6 D5 D4 D3 D2 D1 D0

Read ACFF ARFF —EPROX_OOR E11_OOR E10_OOR E9_OOR E8_OOR

Write — — — — — — — —

GPIO Registers (0x73~0x7A)

GPIO Registers D7 D6 D5 D4 D3 D2 D1 D0

Control Register 0(0x73) GTL0_E11 GTL0_E10 GTL0_E9 GTL0_E8 GTL0_E7 GTL0_E6 GTL0_E5 GTL0_E4

Control Register 1(0x74) GTL1_E11 GTL1_E10 GTL1_E9 GTL1_E8 GTL1_E7 GTL1_E6 GTL1_E5 GTL1_E4

Data Register(0x75) DAT_E11 DAT_E10 DAT_E9 DAT_E8 DAT_E7 DAT_E6 DAT_E5 DAT_E4

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These registers control GPIO and LED driver functions. D7~D0 bits correspond to GPIO and LED functions on ELE11~ ELE4

inputs respectively . When any of these ports are not used for electrode sensing, it can be used for GPIO or LED driver . The GPIO

control registers can be write at anytime regardless Stop Mode or Run mode. The configuration of the LED driver and GPIO

system is described with more detail in application note AN3894.

Note: The number of touch sensing electrodes, and therefore the number of GPIO ports left available is configured by the ECR

(0x5E) and GPIO Enable Register (0x77). ECR has higher priority and overrides the GPIO enabled in 0x77, that is when a pin is

enabled as GPIO but is also selected as electrode by ECR, the GPIO function is di sabled immediately and it becomes an

electrode during Run Mode.

In the S top Mode just after power-on reset, all electrodes and GPIO ports are in high impedance as all the GPIO ports are default

disabled and the electrodes are not enabled.

EN, DIR, CTL0, CTL1: GPIO enable and configuration bits, the functi ons are in description table below.

When the EN bit is set, the corresponding GPIO pin is enabled and the GPIO function is configured by CTL0, CTL1 and DIR bits.

When the port is used as an input, it can be configured as a normal logic input with high impedance (CTL0CTL1 = 2b0 0), input

with internal pull-down (CTL0CTL1 = 2b10) or pullup (CTL0CTL1 = 2b11). Note: the former may result in an unst able lo gic input

state if opened without fixed logic level input.

The GPIO output configuration can be configured as either push pull (CTL0CTL1 = 2b00) or open drain. When the GPIO is used

for LED drivers, the GPIO is set to high side only open drain (CTL0CTL1 = 2b11), which is can source up to 12 mA current into

the LED.

DAT: GPIO Data Register bits.

When a GPIO is enabled as an output, the GPIO port outputs the corresponding DA T bit level from GPIO Data Register (0x075).

The output level toggle remains on during any electrode charging. The level transition will occur after the ADC conversion takes

place. It is important to note that reading this register returns the content of the GPIO Data Register , (not a level of the port). When

a GPIO is configured as input, reading this register returns the latched input level of the corresponding port (not contents of the

GPIO Data Register). Writing to the DAT changes content of the register, but does not effect the input function.

SET: Writing a “1” to this bit will set the corresponding bit in the Data Register.

CLR: Writing a “1” to this bit will clear the corresponding bit in the Data Register.

TOG: Writing a “1” to this bit will toggle the corresponding bit in the Data Register

Writing “1” into the corresponding bits of GPIO Data Set Register , GPIO Data Clear Register , and GPIO Data Toggle Register will

set/clear/toggle contents of the corresponding DAT bit in Data Register. Writing “0” has no meaning. These registers allow any

individual port(s) to be set, cleared, or toggled individually without effecting other ports. It is important to note that reading these

registers returns the contents of the GPIO Data Register reading.

Direction Register(0x76) DIR_E11 DIR_E10 DIR_E9 DIR_E8 DIR_E7 DIR_E6 DIR_E5 DIR_E4

Enable Register(0x77) EN_E11 EN_E10 EN_E9 EN_E8 EN_E7 EN_E6 EN_E5 EN_E4

Data Set Register(0x78) SET_E11 SET_E10 SET_E9 SET_E8 SET_E7 SET_E6 SET_E5 SET_E4

Data Clear Register(0x79) CLR_E11 CLR_E10 CLR_E9 CLR_E8 CLR_E7 CLR_E6 CLR_E5 CLR_E4

Data Toggle Register(0x7A) TOG_E11 TOG_E10 TOG_E11 TOG_E8 TOG_E7 TOG_E6 TOG_E5 TOG_E4

EN DIR CTL0:CTL1 Function Description

0 X XX GPIO function is disabled. Port is high-z state.

1 0 00 GPIO port becomes input port.

1 0 10 GPIO port becomes input port with internal pulldown.

1 0 11 GPIO port becomes input port with internal pullup.

1 0 01 Not defined yet (as same as CTL = 00).

1 1 00 GPIO port becomes CMOS output port.

1 1 11 GPIO port becomes high side only open drain output port for LED driver.

1 1 10 GPIO port becomes low side only open drain output port.

1 1 01 Not defined yet (as same as CTL = 00).

GPIO Registers (0x73~0x7A)

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6 MPR121 Serial Communication

6.1 I2C Serial Communications

The MPR121 uses an I2C Serial Interface.The MPR121 operates as a slave that sends and receives data through an I2C two-

wire interface. The interface uses a Serial Data Line (SDA) and a Serial Clock Line (SCL) to achieve bidirectional communication

between master(s) and slave(s). A master (typically a microcontroller) initiates all data transfers to and from the MPR121, and it

generates the SCL clock that synchronizes the data transfer.

The MPR121 SDA line operates as both an input and an open-drain output. A pullup resistor , typically 4.7 kΩ, is required on SDA.

The MPR121 SCL line operates only as an input. A pullup resistor, typically 4.7 kΩ, is required on SCL if there are multiple

masters on the two-wire interface, or if the master in a single-master system has an open-drain SCL ou tput.

Each transmission consists of a ST AR T condition (Figure 3) sent by a master , followed by the MPR121’s 7-bit slave address plus

R/W bit, a register address byte, one or more data bytes, and finally a STOP condition.

Figure 3. Two-Wire Seria l Inter face Timing Details

6.2 Slave Address

The MPR121 has selectable slave addresses listed by different ADDR pin connections. This also makes it possible for multiple

MPR121 devices to be used together for channel expansions in a single system.

6.3 Operation with Multiple Master

When operating with multiple masters, bus confusion between I2C masters is sometimes a problem. One way to prevent this is

to avoid using repeated starts to the MPR121. On a I2C bus, once a master issues a start/repeated start condition, that master

owns the bus until a stop condition occurs. If a master that does not own the bus attempts to take control of that bus, then

improper addressing may occur . An address may always be rewritten to fix this problem. Follow I2C protocol for multiple master

configurations.

Table 10. MPR121 Slave Address

ADDR Pin Connection I2C Address

VSS 0x5A

VDD 0x5B

SDA 0x5C

SCL 0x5D

SCL

SDA

tLOW

tHIGH

tHD STA

tHD DAT

tHD STA

tSU DAT tSU STA

tBUF

tSU STO

START

CO NDIT IO N

STOP

CO NDIT IO N

REPEATED START

CO NDIT IO N

START

CO NDIT IO N

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6.4 Read and Write Operation Format

< Single Byte Read >

Master ST Device Address [6:0] WRegister Address[7:0] SR Device Address[6:0] R NAK SP

Slave AK AK AK Data[7:0]

< Multiple Byte Read >

Master ST Device Address[6:0] WRegister Ad dress[7:0] SR Device Address[6:0] R AK

Slave AK AK AK Data[7:0]

Master AK AK NAK SP

Slave Data[7:0] Data[7:0] Data[7:0]

< Single Byte Write >

Master ST Device Address[6:0] WRe gister Address[7:0] Data[7:0] SP

Slave AK AK AK

Legend

ST: Start Condition SP: Stop Condition NAK: No Acknowledge W: Write = 0

SR: Repeated Start Condition AK: Acknowledge R: Read = 1

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PACKAGE DIMENSIONS

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Table 11. Revision history

Revision

number Revision

date Description of changes

3 12/2011

• On Page 1, Under Features: Changed 3 mA shutdown current to 3 mA in scan stop mode current, changed

12 electrodes to 12 electrodes/capacitance sensing inputs in which 8 are multifunctional for LED driving and

GPIO, added two new bullets: Integrated independent autocalibration for each electrode input and

Autoconfiguration of charge current and charge time for each electrode input, Under Implementations: added

three bullets

• Updated Table 1 Pin Descriptions, modified pin descriptions for Pins 4, 5, 7

• In Section 3, added Power Supply paragraph, modified remaining paragraphs

• In Table 2, changed ELEPROX to PROX_OOR, changed Register Names from: AFE Configuration and Filter

Configuration to: Filter/Global CDC Configuration and Filter/Global CDT Configuration, added new register for

Soft Reset Register

• Removed AN3889, AN3890, AN3891, AN3892, AN3893, AN3894, AN3895, and AN3944 documents

• Added Sections 5.0 through 6.4

4 02/2013 • Global change to Table 5, renamed all instances Run1 to Run. Added footnote in table

Document Number: MPR121

Rev. 4

02/2013

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