AD9269 Analog Devices, AD9269 Datasheet - Page 29

• Manufacturer Part Number: AD9269
• Description: 16-Bit, 20 MSPS/40 MSPS/65 MSPS/80 MSPS, 1.8 V Dual Analog-to-Digital Converter
• Manufacturer: Analog Devices

Specifications of AD9269

• Resolution (bits): 16bit
• # Chan: 2
• Sample Rate: 80MSPS
• Interface: Par
• Analog Input Type: Diff-Uni
• Ain Range: 2 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

SERIAL PORT INTERFACE (SPI)
The AD9269 serial port interface (SPI) allows the user to configure
the converter for specific functions or operations through a struc-
tured register space provided inside the ADC. The SPI provides
added flexibility and customization, depending on the application.
Addresses are accessed via the serial port and can be written to
or read from via the port. Memory is organized into bytes that
can be further divided into fields, which are documented in the
Memory Map section. For detailed operational information, see
the AN-877 Application Note, Interfacing to High Speed ADCs
via SPI.
CONFIGURATION USING THE SPI
Three pins define the SPI of this ADC: the SCLK, the SDIO, and
the CSB (see Table 14). The SCLK (a serial clock) is used to syn-
chronize the read and write data presented from and to the ADC.
The SDIO (serial data input/output) is a dual-purpose pin that
allows data to be sent to and read from the internal ADC
memory map registers. The CSB (chip select bar) is an active-
low control that enables or disables the read and write cycles.
Table 14. Serial Port Interface Pins
Pin
SCLK
SDIO
CSB
The falling edge of the CSB, in conjunction with the rising edge
of SCLK, determines the start of the framing. An example of the
serial timing and its definitions can be found in Figure 59 and
Table 5.
Other modes involving the CSB are available. The CSB can be
held low indefinitely, permanently enabling the device; this is
called streaming. The CSB can stall high between bytes to allow
for additional external timing. When the CSB is tied high, the
SCLK
SDIO
CSB
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Function
Serial clock. A serial shift clock input that is used to
synchronize serial interface reads and writes.
Serial data input/output. A dual-purpose pin that
typically serves as an input or an output, depending on
the instruction being sent and the relative position in the
timing frame.
Chip select bar. An active-low control that gates the read
and write cycles.
t
S
R/W
t
DS
W1
W0
t
DH
A12
t
HIGH
A11
Figure 59. Serial Port Interface Timing Diagram
t
LOW
A10
A9
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t
CLK
A8
A7
SPI functions are placed in high impedance mode. This mode
turns on any secondary functions of the SPI function pins.
During an instruction phase, a 16-bit instruction is transmitted.
Data follows the instruction phase, and the length of the data
stream is determined by the W1 and W0 bits, as shown in
Figure 59.
All data is composed of 8-bit words. The first bit of the first byte in
a multibyte serial data transfer frame indicates whether a read com-
mand or a write command is issued. This allows the serial data
input/output (SDIO) pin to change direction from an input to
an output at the appropriate point in the serial frame.
In addition to word length, the instruction phase determines
whether the serial frame is a read or write operation, allowing
the serial port to be used both to program the chip and to read
the contents of the on-chip memory. If the instruction is a readback
operation, performing a readback causes the serial data input/
output (SDIO) pin to change direction from an input to an output
at the appropriate point in the serial frame.
Data can be sent in MSB-first mode or in LSB-first mode. MSB
first is the default on power-up and can be changed via the SPI
port configuration register. For more information about this
and other features, see the AN-877 Application Note, Interfacing
to High Speed ADCs via SPI.
HARDWARE INTERFACE
The pins described in Table 14 constitute the physical interface
between the programming device of the user and the serial port
of the AD9269. 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.
D5
D4
D3
D2
D1
D0
t
H
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AD9269
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