ADM1067ASU datasheet(29/32 Pages) AD

29 / 32 page

ADM1067

Rev. B | Page 29 of 32

SMBus PROTOCOLS FOR RAM AND EEPROM

The ADM1067 contains volatile registers (RAM) and nonvolatile

registers (EEPROM). User RAM occupies Address 0x00

to Address 0xDF; EEPROM occupies Address 0xF800 to

Address 0xFBFF.

Data can be written to and read from both RAM and EEPROM

as single data bytes. Data can be written only to unprogrammed

EEPROM locations. To write new data to a programmed loca-

tion, it must first be erased. EEPROM erasure cannot be done at

the byte level. The EEPROM is arranged as 32 pages of 32 bytes

each, and an entire page must be erased.

Page erasure is enabled by setting Bit 2 in the UPDCFG register

(Address 0x90) to 1. If this bit is not set, page erasure cannot

occur, even if the command byte (0xFE) is programmed across

the SMBus.

WRITE OPERATIONS

The SMBus specification defines several protocols for different

types of read and write operations. The following abbreviations

are used in Figure 33 to Figure 41.

•

Start

•

Stop

•

Read

•

W Write

•

Acknowledge

•

No acknowledge

The ADM1067 uses the following SMBus write protocols.

Send Byte

In a send byte operation, the master device sends a single

command byte to a slave device, as follows:

The master device asserts a start condition on SDA.

The master sends the 7-bit slave address followed by the

write bit (low).

The addressed slave device asserts ACK on SDA.

The master sends a command code.

The slave asserts ACK on SDA.

The master asserts a stop condition on SDA and the

transaction ends.

In the ADM1067, the send byte protocol is used for two

purposes:

•

To write a register address to RAM for a subsequent single

byte read from the same address, or a block read or write

starting at that address, as shown in Figure 33.

SLAVE

ADDRESS

RAM

ADDRESS

(0x00 TO 0xDF)

SW A

Figure 33. Setting a RAM Address for Subsequent Read

•

To erase a page of EEPROM memory. EEPROM memory

can be written to only if it is unprogrammed. Before

writing to one or more EEPROM memory locations that

are already programmed, the page or pages containing

those locations must first be erased. EEPROM memory is

erased by writing a command byte.

•

The master sends a command code that tells the slave

device to erase the page. The ADM1067 command code

for a page erasure is 0xFE (1111 1110). Note that, for a

page erasure to take place, the page address has to be given

in the previous write word transaction (see the Write

Byte/Word section). In addition, Bit 2 in the UPDCFG

SLAVE

ADDRESS

COMMAND

BYTE

(0xFE)

Figure 34. EEPROM Page Erasure

As soon as the ADM1067 receives the command byte, page

erasure begins. The master device can send a stop command

as soon as it sends the command byte. Page erasure takes ap-

proximately 20 ms. If the ADM1067 is accessed before erasure

is complete, it responds with a no acknowledge (NACK).

Write Byte/Word

In a write byte/word operation, the master device sends a

command byte and one or two data bytes to the slave device,

as follows:

The master device asserts a start condition on SDA.

The master sends the 7-bit slave address followed by the

write bit (low).

The addressed slave device asserts ACK on SDA.

The master sends a command code.

The slave asserts ACK on SDA.

The master sends a data byte.

The slave asserts ACK on SDA.

The master sends a data byte (or asserts a stop condition at

this point).

The slave asserts ACK on SDA.

10. The master asserts a stop condition on SDA to end the

transaction.

In the ADM1067, the write byte/word protocol is used for three

purposes:

•

To write a single byte of data to RAM. In this case, the

command byte is the RAM address from 0x00 to 0xDF and

the only data byte is the actual data, as shown in Figure 35.

SLAVE

ADDRESS

RAM

ADDRESS

(0x00 TO 0xDF)

W A

DATA

Figure 35. Single Byte Write to RAM

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