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AD5933

Data Sheet

Rev. E | Page 28 of 40

WRITING/READING TO THE AD5933

The interface specification defines several different protocols

for different types of read and write operations. This section

describes the protocols used in the AD5933. The figures in this

section use the abbreviations shown in Table 15.

Table 15. I2C Abbreviation Table

Abbreviation

Condition

Start

Stop

Read

Write

Acknowledge

No acknowledge write byte/command byte

User Command Codes

The command codes in Table 16 are used for reading/writing to

the interface. They are further explained in this section, but are

grouped here for easy reference.

Table 16. Command Codes

Command

Code

Name

Code Description

1010 0000

Block

write

This command is used when writing

multiple bytes to the RAM; see the

Block Write section.

1010 0001

Block

read

This command is used when reading

multiple bytes from RAM/memory;

see the Block Read section.

1011 0000

Address

pointer

This command enables the user to set

the address pointer to any location in

the memory. The data contains the

address of the register to which the

pointer should be pointing reworded

Write Byte/Command Byte

In this operation, the master device sends a byte of data to the

slave device. The write byte can either be a data byte write to a

to a register, the command sequence is as follows (see Figure 30):

1. The master device asserts a start condition on SDA.

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

write bit (low).

3. The addressed slave device asserts an acknowledge on SDA.

4. The master sends a register address.

5. The slave asserts an acknowledge on SDA.

6. The master sends a data byte.

7. The slave asserts an acknowledge on SDA.

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

transaction.

SLAVE

ADDRESS

DATA

Figure 30. Writing Register Data to Register Address

The write byte protocol is also used to set a pointer to an

address (see Figure 31). This is used for a subsequent single-

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

starting at that address.

To set a register pointer, the following sequence is applied:

1. The master device asserts a start condition on SDA.

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

write bit (low).

3. The addressed slave device asserts an acknowledge on

SDA.

4. The master sends a pointer command code (see Table 16;

a pointer command = 1011 0000).

5. The slave asserts an acknowledge on SDA.

6. The master sends a data byte (a register address to where

the pointer is to point).

7. The slave asserts an acknowledge on SDA.

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

transaction.

POINTER

COMMAND

1011 0000

SLAVE

ADDRESS

TO POINT TO

Figure 31. Setting Address Pointer to Register Address

BLOCK WRITE

In this operation, the master device writes a block of data to a

slave device (see Figure 32). The start address for a block write

must previously have been set. In the case of the AD5933 this is

done by setting a pointer to set the register address.

1. The master device asserts a start condition on SDA.

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

write bit (low).

3. The addressed slave device asserts an acknowledge on SDA.

4. The master sends an 8-bit command code (1010 0000) that

tells the slave device to expect a block write.

5. The slave asserts an acknowledge on SDA.

6. The master sends a data byte that tells the slave device the

number of data bytes to be sent to it.

7. The slave asserts an acknowledge on SDA.

8. The master sends the data bytes.

9. The slave asserts an acknowledge on SDA after each

data byte.

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

transaction.

SLAVE

ADDRESS

BLOCK

WRITE

NUMBER

BYTES WRITE

BYTE 0

BYTE 1

BYTE 2

Figure 32. Writing a Block Write

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