MPR081 datasheet(7/22 Pages) FREESCALE

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MPR081

Sensors

Freescale Semiconductor

SERIAL INTERFACE

SERIAL-ADDRESSING

The MPR081 operates as a slave that sends and receives

data through an I2C 2-wire interface. The interface uses a

serial data line (SDA) and a serial clock line (SCL) to achieve

bi-directional communication between master(s) and

slave(s). A master (typically a microcontroller) initiates all

data transfers to and from the MPR081 and generates the

SCL clock that synchronizes the data transfer.

Figure 4. 2-Wire Serial Interface Timing Details

The MPR081 SDA line operates as both an input and an

open-drain output. A pull-up resistor, typically 4.7 k

Ω, is

required on SDA. The MPR081 SCL line operates only as an

input. A pull-up resistor, typically 4.7 k

Ω, is required on SCL if

there are multiple masters on the 2-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 5) sent by a master, followed by the MPR081's 7-bit

slave address plus R/W bit, a register address byte, one or

more data bytes, and finally a STOP condition.

Figure 5. Start and Stop Conditions

START AND STOP CONDITIONS

Both SCL and SDA remain high when the interface is not

busy. A master signals the beginning of a transmission with a

START (S) condition by transitioning SDA from high to low

while SCL is high. When the master has finished

communicating with the slave, it issues a STOP (P) condition

by transitioning SDA from low to high while SCL is high. The

bus is then free for another transmission.

BIT TRANSFER

One data bit is transferred during each clock pulse

(Figure 6). The data on SDA must remain stable while SCL is

high.

Figure 6. Bit Transfer

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