8

SMS2902/SMS2904/SMS2916

2028 5.1 8/2/00

FIGURE 7. PAGE/BYTE WRITE MODE

WRITE OPERATIONS

The SMS29xx allows two types of write operations: byte

write and page write. The byte write operation writes a

page write operation allows up to 16 bytes in the same

Byte WRITE

Upon receipt of both the slave address and word address,

the SMS29xx responds with an ACKnowledge for each.

After receiving the next byte of data, it again responds with

an ACKnowledge. The master then terminates the trans-

fer by generating a STOP condition, at which time the

SMS29xx begins the internal write cycle.

While the internal write cycle is in progress, the SMS29xx

inputs are disabled, and the device will not respond to any

requests from the master. Refer to Figure 7 for the

address, ACKnowledge and data transfer sequence.

Page WRITE

The SMS29xx is capable of a 16-byte page write opera-

tion. 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 SMS29xx

will respond with an ACKnowledge.

The SMS29xx automatically increments the address for

subsequent data words. After the receipt of each word,

the low order address bits are internally incremented by

one. The high order five bits of the address byte remain

constant. Should the master transmit more than 16 bytes,

prior to generating the STOP condition, the address

counter will “roll over,” and the previously written data will

be overwritten. As with the byte-write operation, all inputs

are disabled during the internal write cycle. Refer to

Figure 7 for the address, ACKnowledge and data transfer

sequence.

The next three bits are the high order address bits on the

2904 and 2916 and are “Don’t Care” on the 2902.

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.

D

7

D

6

D

5

D

4

D

3

D

2

D

1

D

0

D

7

D

6

D

5

D

4

D

3

D

2

D

1

D

0

A

7

A

6

A

5

A

4

A

3

A

2

A

1

A

0

D

7

D

5

D

6

D

4

D

0

D

3

D

2

D

1

S

T

A

R

T

Word Address

Data Byte n

Data Byte n+15

S

T

O

P

A

C

K

Acknowledges Transmitted from

SMS29xx to Master Receiver

Slave Address

Device

Type

Address

Read/Write

0= Write

SDA

Bus

Activity

A

C

K

A

C

K

Master Sends Read

Request to Slave

Master Writes Word

Address to Slave

1 0 1 0

0

Data Byte n+1

A

C

K

Master Writes

Data to Slave

Master Transmitter

to

Slave Receiver

Slave Transmitter

to

Master Receiver

Slave Transmitter

to

Master Receiver

Master Transmitter

to

Slave Receiver

Master Transmitter

to

Slave Receiver

Shading Denotes

SMS29xx

SDA Output Active

Master Transmitter

to

Slave Receiver

Slave Transmitter

to

Master Receiver

Slave Transmitter

to

Master Receiver

Master Transmitter

to

Slave Receiver

Slave Transmitter

to

Master Receiver

Master Writes

Data to Slave

Master Writes

Data to Slave

Acknowledges Transmitted from

SMS29xx to Master Receiver

If single byte-write only,

Stop bit issued here.

X

X

R

W

A

10

A

9

A

10

A

9

A

C

K

2028 ILL9.1