
REV. 0
AD7719
–8–
t
12
t
13
t
14
t
15
t
11
t
16
MSB
LSB
CS
SCLK
DIN
Figure 2. Write Cycle Timing Diagram
t
5
t
5A
t
4
t
6
t
3
t
9
MSB
LSB
CS
SCLK
t
8
t
10
t
7
t
6
DOUT
RDY
Figure 3. Read Cycle Timing Diagram
to ensure that a data read is not attempted while the register is
being updated.
CS
is used to select the device. It can be used to
decode the AD7719 in systems where a number of parts are
connected to the serial bus.
Figures 2 and 3 show timing diagrams for interfacing to the
AD7719 with
CS
used to decode the part. Figure 3 is for a read
operation from the AD7719
’
s output shift register while Figure 2
shows a write operation to the input shift register. It is possible
to read the same data twice from the output register even though
the
RDY
line returns high after the first read operation. Care must
be taken, however, to ensure that the read operations have been
completed before the next output update is about to take place.
The AD7719 serial interface can operate in 3-wire mode by
tying the
CS
input low. In this case, the SCLK, DIN, and
DOUT lines are used to communicate with the AD7719 and
the status of RDY bits (RDY0 and RDY1) can be obtained by
interrogating the STATUS Register. This scheme is suitable
for interfacing to microcontrollers. If
CS
is required as a decod-
ing signal, it can be generated from a port bit. For microcontroller
interfaces, it is recommended that the SCLK idles high between
data transfers.
The AD7719 can also be operated with
CS
used as a frame
synchronization signal. This scheme is suitable for DSP inter-
faces. In this case, the first bit (MSB) is effectively clocked out
by
CS
since
CS
would normally occur after the falling edge of
SCLK in DSPs. The SCLK can continue to run between data
transfers provided the timing numbers are obeyed.
DIGITAL INTERFACE
As previously outlined, the AD7719
’
s programmable functions
are controlled using a set of on-chip registers. Data is written to
these registers via the part
’
s serial interface and read access to
the on-chip registers is also provided by this interface. All com-
munications to the part must start with a write operation to the
Communications Register. After power-on or
RESET
, the device
expects a write to its Communications Register. The data writ-
ten to this register determines whether the next operation to the
part is a read or a write operation and also determines to which
register this read or write operation occurs. Therefore, write
access to any of the other registers on the part starts with a write
operation to the Communications Register followed by a write
to the selected register. A read operation from any other register
on the part (including the output data register) starts with a
write operation to the Communications Register followed by a
read operation from the selected register.
The AD7719
’
s serial interface consists of five signals,
CS
, SCLK,
DIN, DOUT, and
RDY
. The DIN line is used for transferring
data into the on-chip registers while the DOUT line is used for
accessing data from the on-chip registers. SCLK is the serial
clock input for the device and all data transfers (either on DIN
or DOUT) take place with respect to this SCLK signal. The
RDY
line is used as a status signal to indicate when data is ready
to be read from the AD7719
’
s data register.
RDY
goes low when a
new data word is available in the output register of either the
main or Aux ADCs. It is reset high when a read operation from
the data register is complete. It also goes high prior to the updating
of the output register to indicate when
not
to read from the device