REV. B
AD5516
–11–
SYNC must be taken high and low again for further serial data
transfer. SYNC may be taken high after the falling edge of the
18th SCLK pulse, observing the minimum SCLK falling edge
to SYNC rising edge time, t
6
. If SYNC is taken high before the
18th falling edge of SCLK, the data transfer will be aborted and
the addressed DAC will not be updated. See the timing diagram
in Figure 1.
Daisy-Chain Mode (DCEN = 1)
I
n Daisy-Chain Mode, the internal gating on SCLK is disabled.
The SCLK is continuously applied to the input shift register
when SYNC is low. If more than 18 clock pulses are applied,
the data ripples out of the shift register and appears on the D
OUT
line. This data is clocked out on the rising edge of SCLK and is
valid on the falling edge. By connecting this line to the D
IN
input on the next device in the chain, a multidevice interface is
constructed. Eighteen clock pulses are required for each device
in the system. Therefore, the total number of clock cycles must
equal 18N, where N is the total number of devices in the chain.
See the timing diagram in Figure 2.
When the serial transfer to all devices is complete, SYNC should
be taken high. This prevents any further data being clocked into the
input shift register. A burst clock containing the exact number of
clock cycles may be used and SYNC taken high some time later.
After the rising edge of SYNC, data is automatically transferred
from each device’s input shift register to the addressed DAC.
RESET Function
The RESET function on the AD5516 can be used to reset all
nodes on this device to their power-on reset condition. This is
implemented by applying a low going pulse of 20 ns minimum
to the RESET Pin on the device.
Table III. Typical Power-On Values
Device Output Voltage
AD5516-1 –0.073 V
AD5516-2 –0.183 V
AD5516-3 –0.391 V
BUSY Output
During conversion, the BUSY output is low and all SCLK pulses
are ignored. At the end of a conversion, BUSY goes high indi-
cating that the update of the addressed DAC is complete. It is
recommended that SCLK is not pulsed while BUSY is low.
MICROPROCESSOR INTERFACING
The AD5516 is controlled via a versatile 3-wire serial interface
that is compatible with a number of microprocessors and DSPs.
AD5516 to ADSP-2106x SHARC DSP Interface
The ADSP-2106x SHARC DSPs are easily interfaced to the
AD5516 without the need for extra logic.
The AD5516 expects a t
3
(SYNC falling edge to SCLK falling
edge setup time) of 15 ns min. Consult the ADSP-2106x User
Manual for information on clock and frame sync frequencies for
the SPORT Register and contents of the TDIV and RDIV Registers.
The user must allow 200 ns (min) between two consecutive
Mode 2 writes in Standalone Mode and 400 ns (min) between
two consecutive Mode 2 writes in Daisy-Chain Mode. During a
Mode 2 operation the BUSY signal remains high.
See Figures 4 and 5 for Mode 1 and Mode 2 data formats.
When MODE bits = 11, the device is in No Operation mode.
This may be useful in daisy-chain applications where the user
does not wish to change the settings of the DACs. Simply write
11 to the MODE bits and the following address and data bits
will be ignored.
SERIAL INTERFACE
The AD5516 has a 3-wire interface that is compatible with
SPI/QSPI/MICROWIRE, and DSP interface standards. Data is
written to the device in 18-bit words. This 18-bit word consists
of two mode bits, four address bits, and 12 data bits as shown
in Figure 4.
The serial interface works with both a continuous and burst
clock. The first falling edge of SYNC resets a counter that counts
the number of serial clocks to ensure the correct number of bits
is shifted in and out of the serial shift registers. In order for
another serial transfer to take place, the counter must be reset
by the falling edge of SYNC.
A3–A0
Four address bits (A3 = MSB Address, A0 = LSB). These are
used to address one of 16 DACs.
Table II. Selected DAC
A3 A2 A1 A0 Selected DAC
0 000 DAC 0
0 001 DAC 1
: :::
1 111 DAC 15
DB11–DB0
These are used to write a 12-bit word into the addressed DAC
register. Figures 1 and 2 show the timing diagram for a write
cycle to the AD5516.
SYNC FUNCTION
In both Standalone and Daisy-Chain Modes, SYNC is an edge-
triggered input that acts as a frame synchronization signal and
chip enable. Data can only be transferred into the device while
SYNC is low. To start the serial data transfer, SYNC should be
taken low observing the minimum SYNC falling to SCLK falling
edge setup time, t
3
.
Standalone Mode (DCEN = 0)
After SYNC goes low, serial data will be shifted into the device’s
input shift register on the falling edges of SCLK for 18 clock
pulses. After the falling edge of the 18th SCLK pulse, data will
automatically be transferred from the input shift register to the
addressed DAC.
