Datasheet

Data Sheet AD7739
Rev. A | Page 21 of 32
DIGITAL INTERFACE DESCRIPTION
HARDWARE
The AD7739 serial interface can be connected to the host
device via the serial interface in several different ways.
The
CS
pin can be used to select the AD7739 as one of several
circuits connected to the host serial interface. When
CS
is high,
the AD7739 ignores the SCLK and DIN signals and the DOUT
pin goes to the high impedance state. When the
CS
signal is not
used, connect the
CS
pin to DGND.
The
RDY
pin can be polled for high-to-low transition or can
drive the host device interrupt input to indicate that the
AD7739 has finished the selected operation and/or new data
from the AD7739 is available. The host system can also wait a
designated time after a given command is written to the device
before reading. Alternatively, the AD7739 status can be polled.
When the
RDY
pin is not used in the system, leave it as an open
circuit. (Note that the
RDY
pin is always an active digital
output, that is, it never goes into a high impedance state.)
The
RESET
pin can be used to reset the AD7739. When not
used, connect this pin to DV
DD
.
The AD7739 interface can be reduced to just two wires connecting
the DIN and DOUT pins to a single bidirectional data line. The
second signal in this 2-wire configuration is the SCLK signal.
The host system must change the data line direction with
reference to the AD7739 timing specification (see the Bus
Relinquish Time in Table 2). The AD7739 cannot operate in the
continuous read mode in 2-wire serial interface configuration.
All the digital interface inputs are Schmitt triggered; therefore,
the AD7739 interface features higher noise immunity and can
be easily isolated from the host system via optocouplers. Figure 12,
Figure 13, and Figure 14 outline some of the possible host device
interfaces: SPI without using the
CS
signal (Figure 12), a DSP
interface (Figure 13), and a 2-wire configuration (Figure 14).
Figure 12. AD7739 to Host Device Interface, SPI
Figure 13. AD7739 to Host Device Interface, DSP
Figure 14. AD7739 to Host Device Interface, 2-Wire Configuration
Figure 15. Serial Interface Signals—Registers Access
SCLK
DIN
DOUT
CS
RDY
RESET
DG
ND
DV
DD
DV
DD
AD7739
SCK
MOSI
MISO
INT
68HC11
SS
03742-0-013
SCLK
DIN
DOUT
CS
RDY
RESET
DV
DD
AD7739
SCLK
DT
DR
INT
TFS
RFS
ADSP-2105
03742-0-001
SCLK
DIN
DOUT
CS
RESET
DG
ND
DV
DD
AD7739
P3.1/TxD
P3.0/RxD
8xC51
03742-0-015
DIN
SCLK
CS
DOUT
WRITE
COMMUNICATIONS
REGISTER
READ
ADC STATUS
REGISTER
03742-0-016