EVAL-AD5765EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD5765EBZ' PDF : 28 Pages View PDF
AD5765
Data Sheet
68HC11 1
MOSI
SCK
PC7
PC6
MISO
AD57651
SDIN
SCLK
SYNC
LDAC
SDO
SDIN
AD57651
SCLK
SYNC
LDAC
SDO
SDIN
AD57651
SCLK
SYNC
LDAC
SDO
The remaining data bits in the write sequence are don’t care.
During the next SPI write, the data appearing on the SDO
output is 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 Figure 4 shows the readback sequence. For
example, to read back the fine gain register of Channel A on the
AD5765, implement the following sequence:
1. Write 0xA0XXXX to the AD5765 input register. This
configures the AD5765 for read mode with the fine gain
register of Channel A selected. Note that all the data bits,
DB15 to DB0, are don’t cares.
2. Follow this 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.
SIMULTANEOUS UPDATING VIA LDAC
1ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 26. Daisy-Chaining the AD5765
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
the system requires 24 clock pulses. Therefore, the total number
of clock cycles must equal 24 N, where N is the total number of
AD5765 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 additional
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 = 1, Bit A2 to Bit A0, in association with Bit
REG2, Bit REG1, and Bit REG0, select the register to be read.
Depending on the status of both SYNC and LDAC, and after
data has been transferred into the input register of the DACs,
there are two ways in which the DAC registers and DAC
outputs can be updated: individually and simultaneously
Individual DAC Updating
In this mode, LDAC is held low while data is clocked into the
input shift register. The addressed DAC output is updated on
the rising edge of SYNC.
Simultaneous Updating of All DACs
In this mode, LDAC is held high while data is clocked into the
input shift register. All DAC outputs are updated by taking
LDAC low any time after SYNC has been taken high. The
update now occurs on the falling edge of LDAC.
OUTPUT
I/V AMPLIFIER
VREFIN
16-BIT
DAC
VOUTx
LDAC
DAC
REGISTER
INPUT
REGISTER
SCLK
SYNC
SDIN
INTERFACE
LOGIC
SDO
Figure 27. Simplified Serial Interface of Input Loading Circuitry
for One DAC Channel
Rev. C | Page 18 of 28
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