AD9910SLASHPCBZ datasheet(46/60 Pages) AD

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AD9910

Rev. 0 | Page 46 of 60

SERIAL PROGRAMMING

CONTROL INTERFACE—SERIAL I/O

The AD9910 serial port is a flexible, synchronous serial commu-

nications port allowing easy interface to many industry-standard

microcontrollers and microprocessors. The serial I/O is compatible

with most synchronous transfer formats, including both the

Motorola 6905/11 SPI and Intel® 8051 SSR protocols.

The interface allows read/write access to all registers that

configure the AD9910. MSB-first or LSB-first transfer formats

are supported. In addition, the serial interface port can be

configured as a single pin input/output (SDIO) allowing a two-

wire interface, or it can be configured as two unidirectional pins

for input/output (SDIO/SDO) enabling a 3-wire interface. Two

optional pins (I/O_RESET and CS) enable greater flexibility for

designing systems with the AD9910.

GENERAL SERIAL I/O OPERATION

There are two phases to a serial communications cycle. The first

is the instruction phase to write the instruction byte into the

AD9910. The instruction byte contains the address of the

section) and also defines whether the upcoming data transfer is

a write or read operation.

For a write cycle, Phase 2 represents the data transfer between

the serial port controller to the serial port buffer. The number

of bytes transferred is a function of the register being accessed.

For example, when accessing the Control Function Register 2

(Address 0x01), Phase 2 requires that four bytes be transferred.

Each bit of data is registered on each corresponding rising edge

of SCLK. The serial port controller expects that all bytes of the

out of sequence for the next communication cycle. However,

one way to write fewer bytes than required is to use the I/O_RESET

pin feature. The I/O_RESET pin function can be used to abort

an I/O operation and reset the pointer of the serial port con-

troller. After an I/O reset, the next byte is the instruction byte.

Note that every completed byte written prior to an I/O reset is

preserved in the serial port buffer. Partial bytes written are not

preserved. At the completion of any communication cycle, the

AD9910 serial port controller expects the next eight rising

SCLK edges to be the instruction byte for the next communi-

cation cycle.

After a write cycle, the programmed data resides in the serial

port buffer and is inactive. I/O_UPDATE transfers data from

the serial port buffer to active registers. The I/O update can

either be sent after each communication cycle or when all serial

operations are complete. In addition, a change in profile pins

can initiate an I/O update.

For a read cycle, Phase 2 is the same as the write cycle with the

following differences: Data is read from the active registers, not

the serial port buffer, and data is driven out on the falling edge

of SCLK.

INSTRUCTION BYTE

The instruction byte contains the following information as

shown in the instruction byte bit map.

Instruction Byte Information Bit Map

MSB

LSB

R/W

R/W—Bit 7 of the instruction byte determines whether a read

or write data transfer occurs after the instruction byte write. Set

indicates read operation. Cleared indicates a write operation.

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

A4, A3, A2, A1, A0—Bit 4, Bit 3, Bit 2, Bit 1, and Bit 0 of the

instruction byte determine which register is accessed during the

data transfer portion of the communications cycle.

SERIAL I/O PORT PIN DESCRIPTIONS

SCLK—Serial Clock

The serial clock pin is used to synchronize data to and from the

AD9910 and to run the internal state machines.

CS—Chip Select Bar

Active low input that allows more than one device on the same

serial communications line. The SDO and SDIO pins 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 (CS) can be tied low in

systems that maintain control of SCLK.

SDIO—Serial Data Input/Output

Data is always written into the AD9910 on this pin. However,

this pin can be used as a bidirectional data line. Bit 1 of CFR1

The default is cleared, which configures the SDIO pin as

bidirectional.

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

AD9910 operates in a single bidirectional I/O mode, this pin

does not output data and is set to a high impedance state.

I/O_RESET—Input/Output Reset

I/O_RESET synchronizes the I/O port state machines without

affecting the addressable registers contents. An active high

input on the I/O_RESET pin causes the current communication

cycle to abort. After I/O_RESET returns low (Logic 0), another

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