AD9211 datasheet(24/29 Pages) AD

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AD9211

Rev. 0 | Page 23 of 28

HARDWARE INTERFACE

Table 9. Serial Port Pins

Mnemonic

Function

The pins described in Table 9 comprise the physical interface

between the user’s programming device and the serial port of

the AD9211. All serial pins are inputs with an open-drain

configuration and should be tied to an external pull-up or pull-

down resistor (suggested value of 10 kΩ).

SCLK

SCLK (Serial Clock) is the serial shift clock in.

SCLK is used to synchronize serial interface

reads and writes.

SDIO

SDIO (Serial Data Input/Output) is a dual-purpose

pin. The typical role for this pin is an input and

output depending on the instruction being sent

and the relative position in the timing frame.

This interface is flexible enough to be controlled by either

PROMS or PIC mirocontrollers as well. This provides the user

with an alternate method to program the ADC other than a SPI

controller.

CSB

CSB (Chip Select Bar) is an active low control that

gates the read and write cycles.

RESET

Master Device Reset. When asserted, device

assumes default settings. Active low.

If the user chooses not to use the SPI interface, some pins serve

a dual function and are associated with a specific function when

strapped externally to AVDD or ground during device power

on. The Configuration Without the SPI section describes the

strappable functions supported on the AD9230.

The falling edge of the CSB, in conjunction with the rising edge

of the SCLK, determines the start of the framing. An example of

the serial timing and its definitions can be found in Figure 51

and Table 11.

CONFIGURATION WITHOUT THE SPI

During an instruction phase, a 16-bit instruction is transmitted.

Data then follows the instruction phase and is determined by

the W0 and W1 bits, which is 1 or more bytes of data. All data is

composed of 8-bit words. The first bit of each individual byte of

serial data indicates whether this is a read or write command.

This allows the serial data input/output (SDIO) pin to change

direction from an input to an output.

In applications that do not interface to the SPI control registers,

the SPI SDIO/DCS and SPI SCLK/DFS pins can alternately

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. In

this mode, the SPI CSB chip select should be connected to

ground, which disables the serial port interface.

Table 10. Mode Selection

Mnemonic

Data may be sent in MSB or in LSB first mode. MSB first is

default on power-up and can be changed by changing the con-

figuration register. For more information about this feature and

others, see the AN-877, Interfacing to High Speed ADCs via SPI.

External

Voltage

Configuration

AVDD

Duty cycle stabilizer enabled

SPI SDIO/DCS

AGND

Duty cycle stabilizer disabled

AVDD

Twos complement enabled

SPI SCLK/DFS

AGND

Offset binary enabled

DON’T CARE

SDIO

SCLK

CSB

tDH

tHI

tCLK

tLO

tDS

R/W

A12

A11

A10

Figure 51. Serial Port Interface Timing Diagram

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