Datasheet

AD5689/AD5687 Data Sheet
Rev. 0 | Page 18 of 24
SERIAL INTERFACE
The AD5689/AD5687 have a 3-wire serial interface (
SYNC
,
SCLK, and SDIN) that is compatible with SPI, QSPI™, and
MICROWIRE® interface standards as well as most DSPs. See
Figure 2 for a timing diagram of a typical write sequence. The
AD5689/AD5687 contain an SDO pin that allows the user to
daisy-chain multiple devices together (see the Daisy-Chain
Operation section) or read back data.
Input Shift Register
The input shift register of the AD5689/AD5687 is 24 bits wide,
and data is loaded MSB first (DB23). The first four bits are the
command bits, C3 to C0 (see Table 9), followed by the 4-bit DAC
address bits, composed of DAC B, DAC A, and two don’t care
bits set to 0 (see Table 8). Finally, the data-word completes the
input shift register.
The data-word comprises 16-bit or 12-bit input code, followed by
zero don’t care bits for the AD5689 or four don’t care bits for the
AD5687, as shown in Figure 38 and Figure 39, respectively.
These data bits are transferred to the input shift register on the
24 falling edges of SCLK and updated on the rising edge of
SYNC
.
Commands can be executed on individual DAC channels or on
both DAC channels, depending on the address bits selected.
Table 8. Address Commands
Address (n)
Selected DAC Channel
DAC B 0 0 DAC A
0 0 0 1 DAC A
1 0 0 0 DAC B
1 0 0 1 DAC A and DAC B
Table 9. Command Definitions
Command
C3 C2 C1 C0 Description
0 0 0 0 No operation
0 0 0 1 Write to Input Register n (dependent on
LDAC
)
0 0 1 0 Update DAC Register n with contents of Input Register n
0 0 1 1 Write to and update DAC Channel n
0 1 0 0 Power down/power up DAC
0 1 0 1 Hardware
LDAC
mask register
0 1 1 0 Software reset (power-on reset)
0 1 1 1 Reserved
1 0 0 0 Set up DCEN register (daisy-chain enable)
1 0 0 1 Set up readback register (readback enable)
1 0 1 0 Reserved
… … … … Reserved
1 1 1 1 Reserved
Figure 38. AD5689 Input Shift Register Content
Figure 39. AD5687 Input Shift Register Content
ADDRESS BITSCOMMAND BITS
DAC
B
0 0
DAC
A
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
C3 C2 C1 C0
DB23 (MSB) DB0 (LSB)
DATA BITS
11255-038
ADDRESS BITSCOMMAND BITS
DAC
B
0 0
DAC
A
D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X
C3 C2 C1 C0
DB23 (MSB) DB0 (LSB)
DATA BITS
11255-039