SMS45 datasheet(14/20 Pages) SUMMIT

14 / 20 page

SMS45

2079 1.2 05/24/04

SUMMIT MICROELECTRONICS, Inc.

Preliminary Information

Figure 10. START and STOP Conditions

2047 Table11 1.0

Table 11. Slave Addresses

START and STOP Conditions

When both the data and clock lines are high the bus is said

to be not busy. A high-to-low transition on the data line,

while the clock is high, is defined as the Start condition.

A low-to-high transition on the data line, while the clock

is high, is defined as the Stop condition. See Figure 10.

Acknowledge (ACK)

Acknowledge is a software convention used to indicate

successful data transfers.

The transmitting device,

either the Master or the Slave, will release the bus after

transmitting eight bits. During the ninth clock cycle the

receiver will pull the SDA line low to Acknowledge that it

received the eight bits of data. The Master will leave the

SDA line high (NACK) when it terminates a read function.

The SMS45 will respond with an Acknowledge after recog-

nition of a Start condition and its slave address byte. If both

the device and a write operation are selected the SMS45

will respond with an Acknowledge after the receipt of each

subsequent 8-Bit word. In the READ mode the SMS45

transmits eight bits of data, then releases the SDA line, and

monitors the line for an Acknowledge signal. If an Acknowl-

edge is detected and no Stop condition is generated by the

Master, the SMS45 will continue to transmit data. If a

NACK is detected the SMS45 will terminate further data

transmissions and await a Stop condition before returning

to the standby power mode.

Device Addressing

Following a Start condition the Master must output the

address of the Slave it is accessing. The most significant

four bits of the Slave address are the device type

identifier/address. For the SMS45 the default is 1010BIN.

The next two bits are the Bus Address. The next bit (the

7th) is the MSB of the memory address.

Read/Write Bit

The last bit of the data stream defines the operation to be

performed. When set to 1 a Read operation is selected;

when set to 0 a Write operation is selected.

WRITE OPERATIONS

The SMS45 allows two types of Write operations: byte

Write and page Write. A byte Write operation writes a

single byte during the nonvolatile write period (tWR). The

page Write operation, limited to the memory array, allows

up to 16 bytes in the same page to be written during tWR.

Byte Write

After the Slave address is sent (to identify the Slave

device and select either a Read or Write operation), a

second byte is transmitted which contains the low order

8 bit address of any one of the 512 words in the array.

Upon receipt of the word address the SMS45 responds with

an Acknowledge. After receiving the next byte of data it

again responds with an Acknowledge. The Master then

terminates the transfer by generating a Stop condition, at

which time the SMS45 begins the internal Write cycle.

While the internal Write cycle is in progress the SMS45

inputs are disabled and the device will not respond to any

requests from the Master.

Page Write (memory only)

The SMS45 is capable of a 16-byte page Write operation.

It is initiated in the same manner as the byte Write

operation, but instead of terminating the Write cycle after

the first data word the Master can transmit up to 15 more

bytes of data. After the receipt of each byte the SMS45 will

respond with an Acknowledge.

The SMS45 automatically increments the address for

subsequent data words. After the receipt of each word the

low order address bits are internally incremented by one.

2047 Fig10

SCL

SDA In

START

Condition

STOP

Condition

)

(

I2C PROGRAMMING INFORMATION (CONTINUED)

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