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PRELIMINARY TECHNICAL DATA

AD9953

R/-Wb—Bit 7 of the instruction byte determines whether a read or write data transfer will occur

after the instruction byte write. Logic high indicates read operation. Logic zero indicates a write

operation.

X, X—Bits 6 and 5 of the instruction byte are don’t care.

A4, A3, A2, A1, A0—Bits 4, 3, 2, 1, 0 of the instruction byte determine which register is accessed

during the data transfer portion of the communications cycle.

Serial Interface Port Pin Description

SCLK — Serial Clock. The serial clock pin is used to synchronize data to and from the AD9953

and to run the internal state machines. SCLK maximum frequency is 25 MHz.

CSB — Chip Select Bar. Active low input that allows more than one device on the same serial

communications line. The SDO and SDIO pins will go to a high impedance state when this input is

high. If driven high during any communications cycle, that cycle is suspended until CS is

reactivated low. Chip Select can be tied low in systems that maintain control of SCLK.

SDIO — Serial Data I/O. Data is always written into the AD9953 on this pin. However, this pin

can be used as a bi-directional data line. Bit 7 of register address 0h controls the configuration of

this pin. The default is logic zero, which configures the SDIO pin as bi-directional.

SDO — Serial Data Out. Data is read from this pin for protocols that use separate lines for

transmitting and receiving data. In the case where the AD9953 operates in a single bi-directional

I/O mode, this pin does not output data and is set to a high impedance state.

SYNCIO — Synchronizes the I/O port state machines without affecting the addressable registers

contents. An active high input on the SYNC I/O pin causes the current communication cycle to

abort. After SYNC I/O returns low (Logic 0) another communication cycle may begin, starting

with the instruction byte write.

MSB/LSB Transqfers

The AD9953 serial port can support both most significant bit (MSB) first or least significant bit

(LSB) first data formats. This functionality is controlled by the Control Register 00h<8> bit. The

default value of Control Register 00h<8> is low (MSB first). When Control Register 00h<8> is set

high, the AD9953 serial port is in LSB first format. The instruction byte must be written in the

format indicated by Control Register 00h<8>. That is, if the AD9953 is in LSB first mode, the

instruction byte must be written from least significant bit to most significant bit.

For MSB first operation, the serial port controller will generate the most significant byte (of the

specified register) address first followed by the next lesser significant byte addresses until the IO

REV. PrB 1/30/03

Page 39

Analog Devices, Inc.

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