AD5744R Analog Devices, AD5744R Datasheet - Page 22

• Manufacturer Part Number: AD5744R
• Description: Complete Quad, 14-Bit, High Accuracy, Serial Input, Bipolar Voltage Output D/A Converter
• Manufacturer: Analog Devices

Specifications of AD5744R

• Resolution (bits): 14bit
• Dac Update Rate: 1MSPS
• Dac Settling Time: 8µs
• Max Pos Supply (v): +16.5V
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD5744R
Daisy-Chain Operation
For systems that contain several devices, the SDO pin can be
used to daisy-chain several devices together. This 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. The 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
*ADDITIONAL PINS OMITTED FOR CLARITY.
68HC11*
MISO
Figure 40. Daisy-Chaining the AD5744R
MOSI
SCK
PC7
PC6
SDIN
SCLK
SYNC
LDAC
SCLK
SYNC
LDAC
SCLK
SYNC
LDAC
AD5744R*
AD5744R*
AD5744R*
SDIN
SDIN
SDO
SDO
SDO
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the system requires 24 clock pulses. Therefore, the total number
of clock cycles must equal 24n, where n is the total number of
AD5744R 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.
Readback Operation
Before a readback operation is initiated, the SDO pin must be
enabled by writing to the function register and clearing the SDO
disable bit; this bit is cleared by default. Readback mode is invoked
by setting the R/ W bit to 1 in the serial input register write.
With R/ W set to 1, Bit A2 to Bit A0, in association with Bit REG2,
to Bit REG0, select the register to be read. The remaining data
bits in the write sequence are don’t care. During the next SPI write,
the data appearing on the SDO output contain the data from the
previously addressed register. For a read of a single register, the
NOP command can be used in clocking out the data from the
selected register on SDO. The readback diagram in
the readback sequence. For example, to read back the fine gain
register of Channel A, implement the following sequence:
1.
2.
Write 0xA0XXXX to the input register. This write configures
the AD5744R for read mode with the fine gain register of
Channel A selected. Note that all the data bits, DB15 to DB0,
are don’t care.
Follow with a second write: an NOP condition, 0x00XXXX.
During this write, the data from the fine gain register is
clocked out on the SDO line; that is, data clocked out contains
the data from the fine gain register in Bit DB5 to Bit DB0.
Data Sheet
Figure 4
shows