Datasheet

Data Sheet AD5121/AD5141
Rev. A | 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
SSSCLKMISO
MICROCONTROLLER
SDI SDO
SCLK
SCLK
R
P
2.2kΩ
R
P
2.2kΩ
SDI SDO
U1 U2
AD5121/
AD5141
AD5121/
AD5141
SYNC
SYNC
DAISY-CHAIN
V
LOGIC
V
LOGIC
10940-046
Figure 39. Daisy-Chain Configuration
DB15
SCLK
SYNC
MOSI
1
2 16
DB0
DB15
SDO_U1
32
DB15
DB0 DB15
DB0
17
18
DB0
INPUT WORD FOR U2
INPUT WORD FOR U1
INPUT WORD FOR U2
UNDEFINED
10940-047
Figure 40. Daisy-Chain Diagram