AD5251/AD5252

Data Sheet

Rev. E | Page 18 of 28

RDAC/EEMEM Quick Commands

The AD5251/AD5252 feature 12 quick commands that facilitate

easy manipulation of RDAC wiper settings and provide RDAC-

to-EEMEM storing and restoring functions. The command

format is shown in Figure 31, and the command descriptions

are shown in Table 9.

When using a quick command, issuing a third byte is not needed,

but is allowed. The quick commands reset and store RDAC to

EEMEM require acknowledge polling to determine whether the

command has finished executing.

the nonvolatile memory. The tolerance of each channel is stored

in the memory during the factory production and can be read

by users at any time. The knowledge of the stored tolerance,

precision, rheostat mode, and open-loop applications in which

knowledge of absolute resistance is critical.

The stored tolerances reside in the read-only memory and are

expressed as percentages. Each tolerance is stored in two memory

locations (see Table 10 ). The tolerance data is expressed in sign

magnitude binary format stored in two bytes; an example is shown

in Figure 32. For the first byte in Register N, the MSB is designated

for the sign (0 = + and 1 = –) and the 7 LSB is designated for the

integer portion of the tolerance.

For the second byte in Register N + 1, all eight data bits are

designated for the decimal portion of tolerance. As shown in

and the data readback from Address 11000 shows 0001 1100

and Address 11001 shows 0000 1111, then RDAC0 tolerance

can be calculated as

MSB: 0 = +

Next 7 MSB: 001 1100 = 28

Tolerance = 28.06% and, therefore,

EEMEM Write-Acknowledge Polling

After each write operation to the EEMEM registers, an

disabled. To determine if the internal write cycle is complete

start condition, followed by the slave address and the write bit.

complete and the interface is ready to proceed with further

until it succeeds. Command 2 and Command 7 also require

acknowledge polling.

EEMEM Write Protection

Setting the

AA

AA

pin to logic low after EEMEM programming

protects the memory and RDAC registers from future write

operations. In this mode, the EEMEM and RDAC read

operations function as normal.

Table 9. RDAC-to-EEMEM Interface and RDAC Operation Quick Command Bits (CMD/

AA

AA

= 1, A2 = 0)

C3

C2

C1

C0

Command Description

0

0

0

0

NOP

0

0

0

1

Restore EEMEM (A1, A0) to RDAC (A1, A0)

24F

1

0

0

1

0

Store RDAC (A1, A0) to EEMEM (A1, A0)

0

0

1

1

Decrement RDAC (A1, A0) 6 dB

0

1

0

0

Decrement all RDACs 6 dB

0

1

0

1

Decrement RDAC (A1, A0) one step

0

1

1

0

Decrement all RDACs one step

0

1

1

1

Reset: restore EEMEMs to all RDACs

1

0

0

0

Increment RDACs (A1, A0) 6 dB

1

0

0

1

Increment all RDACs 6 dB

1

0

1

0

Increment RDACs (A1, A0) one step

1

0

1

1

Increment all RDACs one step

1

1

0

0

Reserved

:

:

:

:

:

:

:

:

:

:

1

1

1

1

Reserved

1

This command leaves the device in the EEMEM read power state, which consumes power. Issue the NOP command to return the device to its idle state.