Datasheet

AD7785
Rev. 0 | Page 21 of 32
0
–20
–40
–60
–80
–100
0 20018016014012010080604020
06721-014
FREQUENCY (Hz)
(dB)
Figure 14. Filter Profile with Update Rate = 16.7 Hz
0
–20
–40
–60
–80
–100
0 30002500200015001000500
06721-015
FREQUENCY (Hz)
(dB)
Figure 15. Filter Profile with Update Rate = 242 Hz
0
–10
–20
–30
–40
–50
–60
0 10000900080007000600050004000300020001000
06721-016
FREQUENCY (Hz)
(dB)
Figure 16. Filter Response at 470 Hz Update Rate
DIGITAL INTERFACE
The programmable functions of the AD7785 are controlled
using a set of on-chip registers. Data is written to these registers
via the serial interface of the device; read access to the on-chip
registers is also provided by this interface. All communications
with the device must start with a write to the communications
register. After power-on or reset, the device expects a write to
its communications register. The data written to this register
determines whether the next operation is a read operation or a
write operation and determines to which register this read or
write operation occurs. Therefore, write access to any of the
other registers on the part begins with a write operation to the
communications register followed by a write to the selected
register. A read operation from any other register (except when
continuous read mode is selected) starts with a write to the
communications register followed by a read operation from the
selected register.
The serial interface of the AD7785 consists of four signals:
CS
,
DIN, SCLK, and DOUT/
RDY
. The DIN line is used to transfer
data into the on-chip registers, and DOUT/
RDY
is used for
accessing from the on-chip registers. SCLK is the serial clock
input for the device, and all data transfers (either on DIN or
DOUT/
RDY
) occur with respect to the SCLK signal. The
DOUT/
RDY
pin operates as a data-ready signal also; the line
going low when a new data-word is available in the output
register. It is reset high when a read operation from the data
register is complete. It also goes high prior to the updating of
the data register to indicate when not to read from the device to
ensure that a data read is not attempted while the register is
being updated.
CS
is used to select a device. It can be used to
decode the AD7785 in systems where several components are
connected to the serial bus.