Datasheet

AD9608
Rev. 0 | Page 32 of 40
HARDWARE INTERFACE
The pins described in Table 15 comprise the physical interface
between the user programming device and the serial port of the
AD9608. The SCLK pin and the CSB pin function as inputs
when using the SPI interface. The SDIO pin is bidirectional,
functioning as an input during write phases and as an output
during readback.
The SPI interface is flexible enough to be controlled by either
FPGAs or microcontrollers. One method for SPI configuration
is described in detail in the AN-812 Application Note, Micro-
controller-Based Serial Port Interface (SPI) Boot Circuit.
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK signal, the CSB signal, and the SDIO signal are typically
asynchronous to the ADC clock, noise from these signals can
degrade converter performance. If the on-board SPI bus is used for
other devices, it may be necessary to provide buffers between
this bus and the AD9608 to prevent these signals from transi-
tioning at the converter inputs during critical sampling periods.
Some pins serve a dual function when the SPI interface is not
being used. When the pins are strapped to DRVDD or ground
during device power-on, they are associated with a specific
function. Table 16 describes the strappable functions supported
on the AD9608.
CONFIGURATION WITHOUT THE SPI
In applications that do not interface to the SPI control registers,
the SDIO/DCS pin, the SCLK/DFS pin, and the PDWN pin
serve as standalone CMOS-compatible control pins. When the
device is powered up, it is assumed that the user intends to use the
pins as static control lines for the duty cycle stabilizer, output
data format, and power-down feature control. In this mode, the
CSB chip select bar should be connected to AVDD, which
disables the serial port interface.
When the device is in SPI mode, the PDWN and OEB pins (if
enabled) remain active. For SPI control of output enable and
power-down, the OEB and PDWN pins should be set to their
default states.
Table 16. Mode Selection
Pin External Voltage Configuration
SDIO/DCS DRVDD (default) Duty cycle stabilizer enabled
AGND Duty cycle stabilizer disabled
SCLK/DFS DRVDD Twos complement enabled
AGND (default) Offset binary enabled
OEB DRVDD Outputs in high impedance
AGND (default) Outputs enabled
PDWN DRVDD
Chip in power-down or
standby
AGND (default) Normal operation
SPI ACCESSIBLE FEATURES
Table 17 provides a brief description of the general features that
are accessible via the SPI. These features are described in detail
in the AN-877 Application Note, Interfacing to High Speed ADCs
via SPI. The AD9608 part-specific features are described in detail
following Table 18, the external memory map register table (see the
Memory Map Register Descriptions section).
Table 17. Features Accessible Using the SPI
Feature
Name
Description
Mode
Allows user to set either power-down mode or
standby mode
Clock
Allows user to access the DCS, set the clock
divider, set the clock divider phase, and enable
the sync
Offset Allows user to digitally adjust the converter offset
Test I/O
Allows user to set test modes to have known
data on output bits
Output Mode Allows user to set the output mode, including LVDS
Output Phase Allows user to set the output clock polarity
Output Delay Allows user to vary the DCO delay