AD7764 Analog Devices, AD7764 Datasheet - Page 25

• Manufacturer Part Number: AD7764
• Description: 24-Bit, 312 kSPS, 109 dB Sigma Delta ADC with On-Chip Buffers and Serial Interface
• Manufacturer: Analog Devices

Specifications of AD7764

• 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

WRITING DATA IN DAISY-CHAIN MODE
Writing to AD7764 devices in daisy-chain mode is similar to
writing to a single device. The serial writing operation is syn-
chronous 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 AD7764 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 imple-
mentation 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 and the
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
AD7764
SDI (D)
Figure 48. Daisy-Chain Write Timing Diagram; Writing to Four AD7764 Devices
MCLK
32 ×
(D)
SDO
t
SCO
Figure 47. Writing to an AD7764 Daisy-Chain Configuration
FSI
SDI
SYNC
AD7764
MCLK
(C)
Rev. A | Page 25 of 32
SDI (C)
SDO
32 ×
t
SCO
rising edge of FSI must be between 32 × (n − 1) to 32 × n SCO
periods. For example, if three AD7764 devices are being written
to in daisy-chain mode, FSI
to 32 × 3 SCO pulses. This means that the rising edge of FSI
must occur between the 64
The AD7764 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 AD7764
device that there are more devices further on in the chain. This
means that the AD7764 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
AD7764
MCLK
(B)
FSI overrides all attempts to read data from the SDO
SDO
SDI (B)
32 ×
t
SCO
FSI
SDI
SYNC
th
AD7764
is logic low for between 32 × (3 − 1)
and 96
MCLK
(A)
SDO
SCO
FSO
th
SCO periods.
SDI (A)
31 ×
t
SCO
AD7764