AD5255 datasheet(13/20 Pages) AD

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AD5255

Rev. 0 | Page 13 of 20

Table 6. RDAC R/W EEPROM Addresses (CMD/ REG = 0, EE/RDAC = 1)

Byte Description

RDAC0 8 LSBs

RDAC0 MSB

RDAC1 8 LSBs

RDAC1 MSB

RDAC2 7 bits

11 bytes RDAC User EEPROM

…to…

Table 7. RDAC Command Table (CMD/REG = 1)

Command Description

NOP

Restore EEPROM to RDAC1

Store RDAC to EEPROM2

Decrement RDAC 6 dB

Decrement All RDACs 6 dB

Decrement RDAC 1 Step

Decrement All RDACs 1 Step

Reset. Restore EEPROM to all RDACs

Increment RDACs 6 dB

Increment All RDACs 6 dB

Increment RDAC 1 Step

Increment All RDAC 1 Step

Reserved

…to…

1 Command leaves the device in the EEPROM read power state. Issue the NOP command to return the device to the idle state.

2 Command requires acknowledge polling after execution.

RDAC Interface Operation

Each programmable resistor wiper setting is controlled by

specific RDAC registers, as shown in Table 5. Each RDAC

provides nonvolatile wiper storage functionality.

RDAC registers and their corresponding EEPROM memory

locations are programmed and read independently from each

other. The RDAC register is refreshed by the EEPROM locations

either with a hardware reset via Pin 1, or by issuing one of the

various RDAC register load commands shown in the Table 7.

RDAC Write

Setting the wiper position requires an RDAC write operation,

shown in Figure 22. RDAC write operations follow a format

similar to the EEPROM write interface. The only difference

between an RDAC write and an EEPROM write operation is the

use of an RDAC address byte in place of the memory address

used in the EEPROM write operation. The RDAC address byte

is described in detail in Table 5 and Table 6.

As with the EEPROM write operation, any RDAC EEPROM

(Shortcut Command 2) write operation disables the I2C

interface during the internal write cycle. Acknowledge polling,

as described in the EEPROM Interface section, is required to

determine whether the write cycle is complete.

RDAC Read

The AD5255 provides two RDAC read operations. The first,

shown in Figure 23, reads the contents of the current RDAC

address counter. Figure 24 illustrates the second read operation,

which allows users to specify which RDAC register to read by

first issuing a “dummy write” command to change the RDAC

address pointer, and then proceeding with the RDAC read

operation at the new address location.

The read-only RDAC EEPROM memory locations can also be

read by using the address and bits specified in Table 6.

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