Datasheet
Table Of Contents
- Proximity Capacitive Touch Sensor Controller
- 1 Pin Descriptions
- 2 Schematic Drawings and Implementation
- 3 Device Operation Overview
- 4 Electrical Characteristics
- 5 Register Operation Descriptions
- 5.1 Register Read/Write Operations and Measurement Run/Stop Mode
- 5.2 Touch Status Registers (0x00~0x01)
- 5.3 Electrode Filtered Data Register (0x04~0x1D)
- 5.4 Baseline Value Register (0x1E~0x2A)
- 5.5 Baseline Filtering Control Register (0x2B~0x40)
- 5.6 Touch / Release Threshold (0x41~0x5A)
- 5.7 Debounce Register (0x5B)
- 5.8 Filter and Global CDC CDT Configuration (0x5C, 0x5D)
- 5.9 Electrode Charge Current Register (0x5F~0x6B)
- 5.10 Electrode Charge Time Register (0x6C~0x72)
- 5.11 Electrode Configuration Register (ECR, 0x5E)
- 5.12 Out-Of-Range Status Registers (0x02, 0x03)
- 5.13 Soft Rest Register (0x80)
- 5.14 GPIO Registers (0x73~0x7A)
- 6 MPR121 Serial Communication
- Disclaimer
MPR121
Sensors
Freescale Semiconductor, Inc. 21
6 MPR121 Serial Communication
6.1 I
2
C Serial Communications
The MPR121 uses an I
2
C Serial Interface.The MPR121 operates as a slave that sends and receives data through an I
2
C 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 output.
Each transmission consists of a START 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 Serial Interface 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 I
2
C masters is sometimes a problem. One way to prevent this is
to avoid using repeated starts to the MPR121. On a I
2
C 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 I
2
C protocol for multiple master
configurations.
Table 10. MPR121 Slave Address
ADDR Pin Connection
I
2
C Address
VSS 0x5A
VDD 0x5B
SDA 0x5C
SCL 0x5D
SCL
SDA
t
LOW
t
HIGH
t
F
t
R
t
HD STA
t
HD DAT
t
HD STA
t
SU DAT
t
SU STA
t
BUF
t
SU STO
ST ART
CONDIT ION
ST O P
CONDIT ION
REPEAT ED ST ART
CONDIT ION
ST ART
CONDIT ION