Data Sheet

AD9681

Rev. A | Page 31 of 40

MEMORY MAP

The AD9681 uses a 3-wire (bidirectional SDIO) interface and 16-bit addressing. Therefore, Bit 0 and Bit 7 in Register 0x00 are set to 0,

and Bit 3 and Bit 4 are set to 1. When Bit 5 in Register 0x00 is set high, the SPI enters a soft reset where all of the user registers revert to

their default values and Bit 2 is automatically cleared.

Table 17. Memory Map Register Table

Reg.

Addr.

(Hex)

Register Name

Bit 7

(MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(LSB)

Default

Value

(Hex)

Comments

Chip Configuration Registers

0x00

SPI port

configuration

0 =

SDIO

active

LSB first

Soft

reset

1 =

16-bit

address

1 =

16-bit

address

Soft

reset

LSB first

0 = SDIO

active

0x18

Nibbles are

mirrored such

that a given

register value

yields the same

function for

either LSB-first

mode or MSB-

first mode.

The default

for ADCs is

16-bit mode.

0x01

Chip ID (global)

8-bit chip ID, Bits[7:0];

0x8F = the AD9681, an octal, 14-bit, 125 MSPS serial LVDS

0x8F

Unique chip ID

used to differ-

entiate devices.

Read only.

0x02

Chip grade (global)

Open

Speed grade ID, Bits[6:4];

110 = 125 MSPS

Open

Open

Open

Open

Read

only

Unique speed

grade ID used

to differentiate

graded devices.

Read only.

Device Index and Transfer Registers

0x05

Device index

Open

Open

DCO±1,

DCO±2

clock

channels

FCO±1,

FCO±2

clock

channels

D1, D2

data

channels

C1, C2

data

channels

B1, B2

data

channels

A1, A2

data

channels

0x3F

Bits are set to

determine

which device

on chip

receives the

next write

command.

The default is

all devices on

chip.

0xFF

Transfer

Open

Open

Open

Open

Open

Open

Open

Initiate

override

0x00

Sets resolution/

sample rate

override.

Global ADC Function Registers

0x08

Power modes

(global)

Open

Open

External

power-

down

pin

function;

0 = full

power-

down,

1 =

standby

Open

Open

Open

Internal power-down

mode, Bits[1:0];

00 = chip run

01 = full power-down

10 = standby

11 = digital reset

0x00

Determines

various generic

modes of chip

operation.

0x09

Clock (global)

Open

Open

Open

Open

Open

Open

Open

Duty

cycle

stabilizer;

0 = off

1 = on

0x01

Turns duty

cycle stabilizer

on or off.

0x0B

Clock divide

(global)

Open

Open

Open

Open

Open

Clock divide ratio, Bits[2:0];

000 = divide by 1

001 = divide by 2

010 = divide by 3

011 = divide by 4

100 = divide by 5

101 = divide by 6

110 = divide by 7

111 = divide by 8

0x00

Divide ratio

is the value

plus 1.