Datasheet

AD7764
Rev. A | Page 25 of 32
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
Writing data to the AD7764 in daisy-chain mode operates with
the same timing structure as writing to a single device (see
FSI
line is low, then the first data bit on the serial
data in the SDI line is latched in on the next SCO falling edge.
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
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
The AD7764 devices can be written to at any time. The falling
edge of
is logic low for between 32 × (3 − 1)
to 32 × 3 SCO pulses. This means that the rising edge of FSI
must occur between the 64
th
and 96
th
SCO periods.
FSI
overrides all attempts to read data from the SDO
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.
SYNC
SDI
FSI
SDO
MCLK
AD7764
(D)
FSI
SYNC
MCLK
SYNC
SDI
FSI
SDO
MCLK
AD7764
(C)
SYNC
SDI
FSI
SDO
MCLK
AD7764
(B)
SYNC
SDI
FSI
MCLK
AD7764
(A)
SDO
FSO
SCO
SDI
06518-020
Figure 47. Writing to an AD7764 Daisy-Chain Configuration
FSI
SCO
SDI (D)
SDI (C) = SDO (D)
SDI (B) = SDO (C)
SDI (A) = SDO (B)
SDI (D)
SDI (C)
SDI (B)
SDI (A)
32 × t
SCO
32 × t
SCO
32 × t
SCO
31 × t
SCO
t
10
06518-021
Figure 48. Daisy-Chain Write Timing Diagram; Writing to Four AD7764 Devices