ADT7462 datasheet(21/92 Pages) AD

21 / 92 page

ADT7462

Rev. 0 | Page 21 of 92

READ OPERATIONS

The ADT7462 uses the following SMBus read protocols.

Receive Byte

The receive byte is useful when repeatedly reading a single

previously. In this operation, the master device receives a single

byte from 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

read bit (high).

The addressed slave device asserts an ACK on SDA.

The master receives a data byte.

The master asserts a NO ACK on SDA.

The master asserts a stop condition on SDA and the

transaction ends.

In the ADT7462, the receive byte protocol is used to read a

single byte of data from a register whose address has previously

been set by a send byte or write byte operation.

SLAVE

ADDRESS

DATA

Figure 31. Single Byte Read from a Register

Block Read

In this operation, the master device reads a block of data from

a slave device. The start address for a block read must have been

set previously, as well as the number of bytes to be read

(maximum = 32). In the case of the ADT7462, the start address

is activated by a send byte operation to set a RAM address. The

number of bytes to be read should be written to the #Bytes bits

in the Configuration 0 register. The block read operation

consists of a send byte operation that sends a block read

command to the slave, immediately followed by a repeated start

and a read operation that reads out multiple data bytes, as

follows:

The master device asserts a start condition on the SDA.

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

write bit (low).

The addressed slave device asserts an ACK on the SDA.

The master sends a command code that tells the slave

device to expect a block read. The ADT7462 command

code for a block read is 0xA1 (1010 0001).

The slave asserts an ACK on SDA.

The master asserts a repeat start condition on the SDA.

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

read bit (high).

The slave asserts an ACK on the SDA.

The ADT7462 sends a byte count telling the master how

many data bytes to expect. The maximum number of bytes

is 32.

10. The master asserts an ACK on SDA.

11. The master receives the expected number of data bytes.

12. The master asserts an ACK on SDA after each data byte.

13. The ADT7462 issues a PEC byte to the master. The master

should check the PEC byte and issue another block read if

the PEC byte is incorrect.

14. A NO ACK is generated after the PEC byte to signal the

end of the read.

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

transaction.

SLAVE

ADDRESS WA

COMMAND

A1h BLOCK

READ

DATA

PEC

BYTE

COUNT A DATA 1 A

SLAVE

ADDRESS

14 15

Figure 32. Block Read from RAM

Note that although the ADT7462 supports packet error

checking (PEC), its use is optional. The PEC byte is calculated

using CRC-8. The frame check sequence (FCS) conforms to

CRC-8 by the polynomial

()

Consult the SMBus 1.1 specifications for more information.

ADT7462 Datasheet(PDF) 21 Page - Analog Devices

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