RX − 8564 LC

13.6. Reading/Writing Data via the I2C Bus Interface

13.6.1. Overview of I2C-BUS

The I2C bus supports bi-directional communications via two signal lines: the SDA (data) line and SCL (clock) line. A combination of these two signals is used to transmit and receive communication start/stop signals, data transfer signals, acknowledge signals, and so on.

Both the SCL and SDA signals are held at high level whenever communications are not being performed.

The starting and stopping of communications is controlled at the rising edge or falling edge of SDA while SCL is at high level.

During data transfers, data changes that occur on the SDA line are performed while the SCL line is at low level, and on the receiving side the data is output while the SCL line is at high level.

The I2C bus device does not include a chip select pin such as is found in ordinary logic devices. Instead of using a chip select pin, slave addresses are allocated to each device and the receiving device responds to communications only when its slave address matches the slave address in the received data. In either case, the data is transferred via the SCL line at a rate of one bit per clock pulse.

13.6.2. System configuration

All ports connected to the I2C bus must be either open drain or open collector ports in order to enable AND connections to multiple devices.

SCL and SDA are both connected to the VDD line via a pull-up resistance. Consequently, SCL and SDA are both held at high level when the bus is released (when communication is not being performed).

VDD

SDA

SCL

Master

 

Slave

 

Master

 

Slave

Transmitter/

 

Transmitter/

 

Transmitter/

 

Transmitter/

Receiver

 

Receiver

 

Receiver

 

Receiver

 

 

 

 

 

 

 

CPU, etc.

[ 8564 ]

 

Other I2C bus device

Any device that controls the data transmission and data reception is defined as a "Master". and any device that is controlled by a master device is defined as a “Slave”.

The device transmitting data is defined as a “Transmitter” and the device receiving data is defined as a receiver”

In the case of this RTC module, controllers such as a CPU are defined as master devices and the RTC module is defined as a slave device. When a device is used for both transmitting and receiving data, it is defined as either a transmitter or receiver depending on these conditions.

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ETM12E-01