AD9856SLASHPCB datasheet(15/37 Pages) AD

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AD9856

Rev. C | Page 14 of 36

Control Bits—Register Address 00h and 01h

SDO Active

—Register Address 00h, Bit 7. Active high indicates

serial port uses dedicated in/out lines. Default low configures

serial port as single-line I/O.

LSB First—

serial port access is LSB-to-MSB format. Default low indicates

MSB-to-LSB format.

REFCLK Multiplier—

form the reference clock multiplier. Valid entries range from

4–20 (decimal). Straight binary to decimal conversion is

implemented. For example, to multiply the reference clock by

19 decimal, Program Register Address 00h, Bits 5–1, as 13h.

Default value is 0A (hex).

Reserved Bit

—Register Address 00h, Bit 0. This bit is reserved.

Always set this bit to Logic 1 when writing to this register.

CIC Gain

—Register Address 01h, Bit 7. The CIC GAIN bit

multiplies the CIC filter output by 2. See the Cascaded

Integrator Comb (CIC) Filter section for more details. Default

value is 0 (inactive).

Continuous Mode

—Register Address 01h, Bit 6 is the

continuous mode configuration bit. Active high configures the

AD9856 to accept continuous-mode timing on the TxENABLE

input. A low configures the device for burst-mode timing.

Default value is 0 (burst mode).

Full Sleep Mode

—Register Address 01h, Bit 5. Active high

full sleep mode bit. When activated, the AD9856 enters a full

shutdown mode, consuming less than 2 mA after completing

a shutdown sequence. Default value is 0 (awake).

Single-Tone Mode

—Register Address 01h, Bit 4. Active high

configures the AD9856 for single-tone applications. The

AD9856 supplies a single-frequency output as determined by

the frequency tuning word (FTW) selected by the active profile.

In this mode, the 12 input data pins are ignored but should be

tied high or low. Default value is 0 (inactive).

Bypass Inverse Sinc Filter

—Register Address 01h, Bit 3.

Active high configures the AD9856 to bypass the SIN(x)/x

compensation filter. Default value is 0 (inverse SINC filter

enabled).

Bypass REFCLK Multiplier

—Register Address 01h, Bit 2.

Active high configures the AD9856 to bypass the REFCLK

multiplier function. When active, effectively causes the

REFCLK multiplier factor to be 1. Default value is 1 (REFCLK

multiplier bypassed).

Input Format Select

—Register Address 01h, Bits 1 and 0, form

the input format mode bits.

10b = 12-bit mode

01b = 6-bit mode

00b = 3-bit mode

Default value is 10b (12-bit mode).

Profile 1 Registers—Active when PROFILE Inputs are 00b

Frequency Tuning Word (FTW)—

The frequency tuning word

for Profile 1 is formed via a concatenation of register addresses

05h, 04h, 03h, and 02h. Bit 7 of Register Address 05h is the

most significant bit of the Profile 1 frequency tuning word. Bit 0

of Register Address 02h is the least significant bit of the Profile

1 frequency tuning word. The output frequency equation is

given as: fOUT = (FTW SYSCLK)/232.

Interpolation Rate—

form the Profile 1 CIC filter interpolation rate value. Allowed

values range from 2 to 63 (decimal).

Spectral Inversion—

high, Profile 1 spectral inversion bit. When active, inverted

modulation is performed [I Cos(ωt) + Q × Sin( t)]. The

Default is inactive, Logic 0, noninverted modulation

[I × Cos(ωt) − Q × Sin(ωt)].

Bypass Half-Band Filter 3

—Register Address 06h, Bit 0.

Active high, causes the AD9856 to bypass the third half-band

filter stage that precedes the CIC interpolation filter. Bypassing

the third half-band filter negates the 2× upsample inherent with

this filter and reduces the overall interpolation rate of the half-

band filter chain from 8× to 4×. Default value is 0 (Half-Band 3

enabled).

AD8320/AD8321 Gain Control

—Register Address 07h, Bit 7

through Bit 0 form the Profile 1 AD8320/AD8321 gain bits.

The AD9856 dedicates three output pins, which directly

interface to the AD8320/AD8321 cable driver amp. This

allows direct control of the cable driver via the AD9856. See

the Error! Reference source not found. section for more

details. Bit 7 is the MSB, Bit 0 is the LSB. Default value is 00h.

Profile 2 Registers—Active when PROFILE Inputs are 01b

Profile 2 register functionality is identical to Profile 1, with the

exception of the register addresses.

Profile 3 Registers—Active when PROFILE Inputs are 10b

Profile 3 register functionality is identical to Profile 1, with the

exception of the register addresses.

Profile 4 Registers—Active when PROFILE Inputs are 11b

Profile 4 register functionality is identical to Profile 1, with the

exception of the register addresses.

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