DS1306

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SERIAL INTERFACE

The DS1306 offers the flexibility to choose between two serial interface modes. The DS1306 can

communicate with the SPI interface or with a standard 3-wire interface. The interface method used is

When this pin is connected to ground, standard 3-wire communication is selected.

SERIAL PERIPHERAL INTERFACE (SPI)

The serial peripheral interface (SPI) is a synchronous bus for address and data transfer and is used when

interfacing with the SPI bus on specific Motorola microcontrollers such as the 68HC05C4 and the

Four pins are used for the SPI. The four pins are the SDO (serial data out), SDI (serial data in), CE (chip

enable), and SCLK (serial clock). The DS1306 is the slave device in an SPI application, with the

microcontroller being the master.

The SDI and SDO pins are the serial data input and output pins for the DS1306, respectively. The CE

input is used to initiate and terminate a data transfer. The SCLK pin is used to synchronize data

movement between the master (microcontroller) and the slave (DS1306) devices.

The shift clock (SCLK), which is generated by the microcontroller, is active only during address and data

transfer to any device on the SPI bus. The inactive clock polarity is programmable in some

microcontrollers. The DS1306 determines on the clock polarity by sampling SCLK when CE becomes

active. Therefore either SCLK polarity can be accommodated. Input data (SDI) is latched on the internal

strobe edge and output data (SDO) is shifted out on the shift edge (Figure 5). There is one clock for each

bit transferred. Address and data bits are transferred in groups of eight, MSB first.

Figure 5. SERIAL CLOCK AS A FUNCTION OF MICROCONTROLLER

CLOCK POLARITY (CPOL)

CE

CPOL = 1

SCLK

DATA LATCH (WRITE)

SHIFT DATA OUT (READ)

CPOL = 0

SCLK

DATA LATCH (WRITE)

SHIFT DATA OUT (READ)

NOTE 1: CPHA BIT POLARITY (IF APPLICABLE) MAY NEED TO BE SET ACCORDINGLY.

NOTE 2: CPOL IS A BIT THAT IS SET IN THE MICROCONTROLLER’S CONTROL REGISTER.

NOTE 3: SDO REMAINS AT HIGH-Z UNTIL 8 BITS OF DATA ARE READY TO BE SHIFTED OUT DURING A READ.