AD9992BBCZ datasheet(72/92 Pages) AD

72 / 92 page

AD9992

Rev. C | Page 72 of 92

SERIAL INTERFACE TIMING

The internal registers of the AD9992 are accessed through a

3-wire serial interface. Each register consists of a 12-bit address

and a 28-bit data-word. Both the 12-bit address and 28-bit data-

word are written starting with the LSB. To write to each register,

a 40-bit operation is required, as shown in Figure 83. Although

many registers are fewer than 28 bits wide, all 28 bits must be

written for each register. For example, if the register is only 20 bits

wide, the upper eight bits are don’t cares and must be filled with

0s during the serial write operation. If fewer than 28 data bits are

written, the register is not updated with new data.

Figure 84 shows a more efficient way to write to the registers,

using the AD9992 address autoincrement capability. Using this

method, the lowest desired address is written first, followed by

multiple 28-bit data-words. Each new 28-bit data-word is

automatically written to the next highest register address. By

eliminating the need to write each 12-bit address, faster register

loading is achieved. Continuous write operations can be used

starting with any register location.

SDATA

A10 A11

D25

D26 D27

tLS

tDS

12-BIT ADDRESS

28-BIT DATA

tLH

tDH

SCK

NOTES

1. SDATA BITS ARE LATCHED ON SCK RISING EDGES. SCK CAN IDLE HIGH OR LOW BETWEEN WRITE OPERATIONS.

2. ALL 40 BITS MUST BE WRITTEN: 12 BITS FOR ADDRESS AND 28 BITS FOR DATA.

3. IF THE REGISTER LENGTH IS <28 BITS, 0s MUST BE USED TO COMPLETE THE 28-BIT DATA LENGTH.

4. NEW DATA VALUES ARE UPDATED IN THE SPECIFIED REGISTER LOCATION AT DIFFERENT TIMES, DEPENDING ON THE

PARTICULAR REGISTER WRITTEN TO. SEE THE UPDATING OF NEW REGISTER VALUES SECTION FOR MORE INFORMATION.

Figure 83. Serial Write Operation

SDATA

A10 A11

D26 D27

SCK

NOTES

1. MULTIPLE SEQUENTIAL REGISTERS CAN BE LOADED CONTINUOUSLY.

2. THE FIRST (LOWEST) REGISTER ADDRESS IS WRITTEN, FOLLOWED BY MULTIPLE 28-BIT DATA-WORDS.

3. THE ADDRESS AUTOMATICALLY INCREMENTS WITH EACH 28-BIT DATA-WORD (ALL 28 BITS MUST BE WRITTEN).

4. SL IS HELD LOW UNTIL THE LAST DESIRED REGISTER HAS BEEN LOADED.

D26

D27

DATA FOR STARTING

DATA FOR NEXT

Figure 84. Continuous Serial Write Operation

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