AD9854AST datasheet(36/52 Pages) AD

36 / 52 page

AD9854

Rev. E | Page 36 of 52

GENERAL OPERATION OF THE SERIAL INTERFACE

There are two phases of a serial communication cycle with the

AD9854. Phase 1 is the instruction cycle, which is the writing of

an instruction byte into the AD9854 coincident with the first

eight SCLK rising edges. The instruction byte provides the

AD9854 serial port controller with information regarding the

data transfer cycle, which is Phase 2 of the communication

cycle. The Phase 1 instruction byte defines whether the

upcoming data transfer is a read or write and the register

address to be acted upon.

The first eight SCLK rising edges of each communication cycle

are used to write the instruction byte into the AD9854. The

remaining SCLK edges are for Phase 2 of the communication

cycle. Phase 2 is the actual data transfer between the AD9854

and the system controller. The number of data bytes transferred

in Phase 2 of the communication cycle is a function of the

transferred.) The AD9854 internal serial I/O controller expects

every byte of the register being accessed to be transferred.

Therefore, the user should write between I/O update clocks.

At the completion of a communication cycle, the AD9854 serial

port controller expects the subsequent eight rising SCLK edges

to be the instruction byte of the next communication cycle. In

addition, an active high input on the IO RESET pin immediately

terminates the current communication cycle. After IO RESET

returns low, the AD9854 serial port controller requires the

subsequent eight rising SCLK edges to be the instruction byte

of the next communication cycle.

All data input to the AD9854 is registered on the rising edge of

SCLK, and all data is driven out of the AD9854 on the falling

edge of SCLK.

Figure 54 and Figure 55 show the general operation of the

AD9854 serial port.

Table 10. Register Address vs. Data Bytes Transferred

Serial Register Address

Number of Bytes Transferred

Phase Offset Tuning Word Register 1

Phase Offset Tuning Word Register 2

Frequency Tuning Word 1

Frequency Tuning Word 2

Delta frequency register

Update clock rate register

Ramp rate clock register

Control register

I path digital multiplier register

Q path digital multiplier register

Shaped on/off keying ramp rate register

Q DAC register

INSTRUCTION

CYCLE

DATA TRANSFER

INSTRUCTION

BYTE

DATA BYTE 1

DATA BYTE 2

DATA BYTE 3

SDIO

Figure 54. Using SDIO as a Read/Write Transfer

INSTRUCTION

CYCLE

DATA TRANSFER

INSTRUCTION

BYTE

SDIO

DATA TRANSFER

DATA BYTE 1

DATA BYTE 2

DATA BYTE 3

SDO

Figure 55. Using SDIO as an Input and SDO as an Output

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