AD7765 Analog Devices, AD7765 Datasheet - Page 24

• Manufacturer Part Number: AD7765
• Description: 24-Bit, 156 kSPS, 112 dB Sigma-Delta ADC with On-Chip Buffers and Serial Interface
• Manufacturer: Analog Devices

Specifications of AD7765

• Resolution (bits): 24bit
• # Chan: 1
• Sample Rate: 40MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: 6.5 V p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

AD7765
WRITING DATA IN DAISY-CHAIN MODE
Writing to AD7765 devices in daisy-chain mode is similar to
writing to a single device. The serial writing operation is
synchronous to the SCO signal. The status of the frame synchro-
nization input, FSI , is checked on the falling edge of the SCO
signal. If the
data in the SDI line is latched in on the next SCO falling edge.
Writing data to the AD7765 in daisy-chain mode operates with
the same timing structure as writing to a single device (see
Figure 3). The difference between writing to a single device
and writing to a number of daisy-chained devices is in the
implementation of the FSI signal. The number of devices that
are in the daisy chain determines the period for which the FSI
signal must remain logic low. To write to n number of devices
in the daisy chain, the period between the falling edge of FSI
SDI (C) = SDO (D)
SDI (B) = SDO (C)
SDI (A) = SDO (B)
SDI (D)
SCO
FSI
FSI line is low, then the first data bit on the serial
MCLK
SYNC
SDI
FSI
t
10
FSI
SDI
SYNC
AD7765
SDI (D)
Figure 42. Daisy-Chain Write Timing Diagram; Writing to Four AD7765 Devices
MCLK
32 ×
(D)
SDO
t
SCO
Figure 41. Writing to an AD7765 Daisy-Chain Configuration
FSI
SDI
SYNC
AD7765
MCLK
(C)
Rev. A | Page 24 of 32
SDI (C)
SDO
32 ×
t
SCO
and the rising edge of FSI must be between 32 × (n − 1) to 32 ×
n SCO periods. For example, if three AD7765 devices are being
written to in daisy-chain mode, FSI
32 × (3 − 1) to 32 × 3 SCO pulses. This means that the rising
edge of FSI must occur between the 64
The AD7765 devices can be written to at any time. The falling
edge of
pin. In the case of a daisy chain, the FSI signal remaining logic
low for more than 32 SCO periods indicates to the AD7765
device that there are more devices further on in the chain. This
means that the AD7765 directs data that is input on the SDI pin
to its SDO pin. This ensures that data is passed to the next
device in the chain.
FSI
SDI
SYNC
AD7765
MCLK
(B)
FSI overrides all attempts to read data from the SDO
SDO
SDI (B)
32 ×
t
SCO
FSI
SDI
SYNC
AD7765
MCLK
(A)
SDO
FSO
is logic low for between
SDI (A)
th
31 ×
and 96
t
SCO
th
SCO period.