AD5121 datasheet(21/32 Pages) AD

21 / 32 page

Data Sheet

AD5121/AD5141

Rev. 0 | Page 21 of 32

Daisy-Chain Connection

Daisy chaining minimizes the number of port pins required from

the controlling IC. As shown in Figure 39, the SDO pin of one

package must be tied to the SDI pin of the next package. The clock

period may need to be increased because the propagation delay

of the line between subsequent devices. When two AD5121/

AD5141 devices are daisy chained, 32 bits of data are required.

The first 16 bits assigned to U2, and the second 16 bits assigned

to U1, as shown in Figure 40. Keep the SYNC pin low until all

32 bits are clocked into their respective serial registers. The SYNC

pin is then pulled high to complete the operation. A typical

connection is shown in Figure 39.

To prevent data from mislocking (for example, due to noise) the

part includes an internal counter, if the clock falling edges count

is not a multiple of 8, the part ignores the command. A valid

clock count is 16, 24, or 32. The counter resets when SYNC

returns high.

MOSI

SCLK

MISO

MICROCONTROLLER

SDI

SDO

SCLK

2.2k

Ω

2.2k

Ω

SDI

SDO

AD5121/

AD5141

AD5121/

AD5141

SYNC

VLOGIC

Figure 39. Daisy-Chain Configuration

DB15

SCLK

SYNC

MOSI

DB0

DB15

SDO_U1

DB15

DB0

DB15

DB0

INPUT WORD FOR U2

INPUT WORD FOR U1

INPUT WORD FOR U2

UNDEFINED

Figure 40. Daisy-Chain Diagram

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