AD5780ACPZ AD [Analog Devices], AD5780ACPZ Datasheet - Page 20

• Manufacturer Part Number: AD5780ACPZ
• Manufacturer: AD [Analog Devices]

AD5780
Standalone Operation
The serial interface works with both a continuous and noncon-
tinuous serial clock. A continuous SCLK source can be used
only if SYNC is held low for the correct number of clock cycles.
In gated clock mode, a burst clock containing the exact number
of clock cycles must be used, and SYNC must be taken high after
the final clock to latch the data. The first falling edge of SYNC
starts the write cycle. Exactly 24 falling clock edges must be
applied to SCLK before SYNC is brought high again. If SYNC is
brought high before the 24
is invalid. If more than 24 falling SCLK edges are applied before
SYNC is brought high, the input data is also invalid.
The input shift register is updated on the rising edge of SYNC .
For another serial transfer to take place, SYNC must be brought
low again. After the end of the serial data transfer, data is
automatically transferred from the input shift register to the
addressed register. When the write cycle is complete, the output
can be updated by taking LDAC low while SYNC is high.
Daisy-Chain Operation
For systems that contain several devices, the SDO pin can be
used to daisy-chain several devices together. Daisy-chain mode
can be useful in system diagnostics and in reducing the number
of serial interface lines. The first falling edge of SYNC starts the
write cycle. SCLK is continuously applied to the input shift register
when SYNC is low. If more than 24 clock pulses are applied, the
data ripples out of the shift register and appears on the SDO
line. This data is clocked out on the rising edge of SCLK and
is valid on the falling edge. By connecting the SDO of the first
device to the SDIN input of the next device in the chain, a
multidevice interface is constructed. Each device in the system
requires 24 clock pulses. Therefore, the total number of clock
cycles must equal 24 × N, where N is the total number of
AD5780 devices in the chain. When the serial transfer to all
devices is complete, SYNC is taken high. This latches the input
data in each device in the daisy chain and prevents any further
data from being clocked into the input shift register. The serial
clock can be a continuous or a gated clock.
A continuous SCLK source can be used only if SYNC is held
low for the correct number of clock cycles. In gated clock mode,
a burst clock containing the exact number of clock cycles must
be used, and SYNC must be taken high after the final clock to
latch the data.
In any one daisy-chain sequence, do not mix writes to the DAC
register with writes to any of the other registers. All writes to the
daisy-chained parts must be either writes to the DAC registers
or writes to the control, clearcode, or software control register.
th
falling SCLK edge, the data written
Rev. C | Page 20 of 28
Readback
The contents of all the on-chip registers can be read back via
the SDO pin. Table 7 outlines how the registers are decoded.
After a register has been addressed for a read, the next 24 clock
cycles clock the data out on the SDO pin. The clocks must be
applied while SYNC is low. When SYNC is returned high, the
SDO pin is placed in tristate. For a read of a single register, the
NOP function can be used to clock out the data. Alternatively,
if more than one register is to be read, the data of the first
register to be addressed can be clocked out at the same time
that the second register to be read is being addressed. The SDO
pin must be enabled to complete a readback operation. The
SDO pin is enabled by default.
HARDWARE CONTROL PINS
Load DAC Function ( LDAC )
After data has been transferred into the input register of the
DAC, there are two ways to update the DAC register and DAC
output. Depending on the status of both SYNC and LDAC , one
of two update modes is selected: synchronous DAC update or
asynchronous DAC update.
Synchronous DAC Update
In this mode, LDAC is held low while data is being clocked into
the input shift register. The DAC output is updated on the rising
edge of SYNC .
CONTROLLER
SERIAL CLOCK
CONTROL OUT
DATA IN
DATA OUT
*ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 51. Daisy-Chain Block Diagram
SDIN
SCLK
SYNC
SCLK
SYNC
SCLK
SYNC
AD5780*
AD5780*
AD5780*
SDIN
SDIN
SDO
SDO
SDO
Data Sheet