AD9856SLASHPCB datasheet(26/32 Pages) AD

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AD9856

–26–

REV. B

PROGRAMMING/WRITING THE AD8320/AD8321 CABLE

DRIVER AMPLIFIER GAIN CONTROL

Programming the Gain Control register of the AD8320/AD8321

programmable cable driver amplifier can be accomplished via

the AD9856 serial port. Four 8-bit registers (one per profile)

within the AD9856 store the gain value to be written to the

AD8320/AD8321. The AD8320/AD8321 is written via three

dedicated AD9856 output pins that are directly connected to

the AD8320/AD8321’s serial input port. The transfer of data

from the AD9856 to the AD8320/AD8321 requires 136 SYSCLK

clock cycles and occurs upon detection of three conditions.

Each is described below:

1. Power-up Reset—Upon initial power up, the AD9856 clears

(Logic 0) the contents of control registers 07h, 0Dh, 13h,

and 19h, which defines the lowest gain setting of the AD8320/

AD8321. Thus, the AD9856 writes all 0s out of the AD8320/

AD8321 serial interface.

SYMBOL

DEFINITION

MIN

tPRE

CS SETUP TIME

30ns

tSCLK

PERIOD OF SERIAL DATA CLOCK

100ns

tDSU

SERIAL DATA SETUP TIME

30ns

tSCLKPWH

SERIAL DATA CLOCK PULSEWIDTH HIGH

40ns

tSCLKPWL

SERIAL DATA CLOCK PULSEWIDTH LOW

40ns

tDHLD

SERIAL DATA HOLD TIME

0ns

SCLK

SDIO

1ST BIT

2ND BIT

tDSU

tDHLD

tSCLKPWH

tSCLKPWL

tSCLK

tPRE

Figure 38. Timing Diagram for Data Write to AD9856

SYMBOL

DEFINITION

MAX

tDV

DATA VALID TIME

30ns

SCLK

SDIO

1ST BIT

2ND BIT

tDV

SDO

Figure 39. Timing Diagram for Read from AD9856

2. Change in profile selection bits (PS1, PS0)—The AD9856

samples the PS1, PS0 input pins and writes to the AD8320/

AD8321 gain control register when a change in profile is

determined. The data written to the AD8320/AD8321 comes

from the AD9856 gain control register associated with the

current profile.

3. Serial Port Write of AD9856 Registers that Contain

AD8320/AD8321 Data—The AD9856 will write to the

AD8320/AD8321 with data from the gain control register

associated with the current profile whenever ANY AD9856

gain control register is updated. The user does not have to

write the AD9856 in any particular order or be concerned

with time between writes. If the AD9856 is currently writ-

ing to the AD8320/AD8321 while one of the four AD9856

gain control registers is being addressed, the AD9856 will

immediately terminate the AD8320/AD8321 write sequence

(without updating the AD8320/AD8321) and begin a new

AD8320/AD8321 write sequence.

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