DS3232M datasheet(20/23 Pages) MAXIM

20 / 23 page

DS3232M

±5ppm, I2C Real-Time Clock with SRAM

Maxim Integrated

I2C Serial Port Operation

I2C Slave Address

The device’s slave address byte is D0h. The first byte

sent to the device includes the device identifier, device

address, and the R/W bit (Figure 9). The device address

sent by the I2C master must match the address assigned

to the device.

I2C Definitions

The following terminology is commonly used to describe

I2C data transfers.

Master Device: The master device controls the slave

devices on the bus. The master device generates SCL

clock pulses and START and STOP conditions.

Slave Devices: Slave devices send and receive data

at the master’s request.

Bus Idle or Not Busy: Time between STOP and

START conditions when both SDA and SCL are inac-

tive and in their logic-high states. When the bus is idle,

it often initiates a low-power mode for slave devices.

START Condition: A START condition is generated

by the master to initiate a new data transfer with a

slave. Transitioning SDA from high to low while SCL

remains high generates a START condition. See

Figure 1 for applicable timing.

STOP Condition: A STOP condition is generated

by the master to end a data transfer with a slave.

Transitioning SDA from low to high while SCL remains

high generates a STOP condition. See Figure 1 for

applicable timing.

Repeated START Condition: The master can use

a repeated START condition at the end of one data

transfer to indicate that it immediately initiates a new

data transfer following the current one. Repeated

STARTs are commonly used during read operations

to identify a specific memory address to begin a data

transfer. A repeated START condition is issued identi-

cally to a normal START condition. See Figure 1 for

applicable timing.

Bit Write: Transitions of SDA must occur during

the low state of SCL. The data on SDA must remain

valid and unchanged during the entire high pulse of

SCL plus the setup and hold time requirements (see

Figure 1). Data is shifted into the device during the

rising edge of the SCL.

Bit Read: At the end of a write operation, the master

must release the SDA bus line for the proper amount

of setup time (see Figure 1) before the next rising

edge of SCL during a bit read. The device shifts out

each bit of data on SDA at the falling edge of the pre-

vious SCL pulse and the data bit is valid at the rising

edge of the current SCL pulse. Remember that the

master generates all SCL clock pulses including when

it is reading bits from the slave.

Acknowledge (ACK and NACK): An acknowledge

(ACK) or not acknowledge (NACK) is always the ninth

bit transmitted during a byte transfer. The device

receiving data (the master during a read or the slave

during a write operation) performs an ACK by trans-

mitting a 0 during the ninth bit. A device performs

a NACK by transmitting a 1 during the ninth bit.

Timing for the ACK and NACK is identical to all other

bit writes. An ACK is the acknowledgment that the

device is properly receiving data. A NACK is used to

terminate a read sequence or as an indication that the

device is not receiving data.

Byte Write: A byte write consists of 8 bits of informa-

tion transferred from the master to the slave (most

significant bit first) plus a 1-bit acknowledgment from

the slave to the master. The 8 bits transmitted by the

master are done according to the bit write definition

and the acknowledgment is read using the bit read

definition.

Byte Read: A byte read is an 8-bit information transfer

from the slave to the master plus a 1-bit ACK or NACK

from the master to the slave. The 8 bits of information

that are transferred (most significant bit first) from the

slave to the master are read by the master using the

bit read definition, and the master transmits an ACK

using the bit write definition to receive additional data

bytes. The master must NACK the last byte read to

terminate communication so the slave returns control

of SDA to the master.

Figure 9. I2C Slave Address Byte

0R/W

MSB

LSB

READ/

WRITE BIT

DEVICE

IDENTIFIER

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