AD9789BBCZ datasheet(24/76 Pages) AD

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AD9789

Rev. A | Page 24 of 76

Read

If the instruction word is for a read operation, the next N × 8

SCLK cycles clock out the data from the address specified in the

instruction word, where N is 1 to 3 as determined by Bits[N1:N0].

If N = 4, the read operation is in streaming mode, continuing

until CS is raised. Streaming mode does not skip over reserved

or blank registers. The readback data is valid on the falling edge

of SCLK.

The default mode of the AD9789 serial control port is the uni-

directional mode. In unidirectional mode, the readback data

appears on the SDO pin. It is also possible to set the AD9789 to

bidirectional mode using the SDIO_DIR bit (Register 0x00[7]).

In bidirectional mode, both the sent data and the readback data

appear on the SDIO pin.

A readback request reads the data that is in the serial control port

buffer area or the data in the active registers (see Figure 63).

The AD9789 supports only the long instruction mode; therefore,

Long instruction mode is the default at power-up or reset, and

writing to these bits has no effect.

The AD9789 uses Register Address 0x00 to Register Address 0x55.

SERIAL

CONTROL

PORT

SCLK

SDO

SDIO

FREQNEW

WRITE REGISTER 0x1E = 0x10

TO UPDATE REGISTERS

Figure 63. Relationship Between Serial Control Port Buffer Registers and

Active Registers of the AD9789

INSTRUCTION WORD (16 BITS)

The MSB of the instruction word is R/W, which indicates

whether the instruction is a read or a write. The next two bits,

N1 and N0, indicate the length of the transfer in bytes. The final

13 bits (Bits[A12:A0]) are the address at which to begin the read

or write operation.

For a write, the instruction word is followed by the number of

bytes of data indicated by Bits[N1:N0] (see Table 7).

Table 7. Byte Transfer Count

Bytes to Transfer

Streaming mode

Bits[A12:A0] select the address within the register map that is

written to or read from during the data transfer portion of the

communication cycle. Only Bits[A6:A0] are needed to cover the

range of the 0x55 registers used by the AD9789. Bits[A12:A7]

must always be 0. For multibyte transfers, this address is the

starting byte address. In MSB first mode, subsequent bytes

increment the address.

MSB/LSB FIRST TRANSFERS

The AD9789 instruction word and byte data can be MSB first or

LSB first. Any data written to Register 0x00 must be mirrored,

the upper four bits (Bits[7:4]) with the lower four bits (Bits [3:0]).

This makes it irrelevant whether LSB first or MSB first is in

effect. As an example of this mirroring, the default setting for

bits set the long instruction mode (the default and the only

mode supported). The default for the AD9789 is MSB first.

When LSB first is set by Register 0x00[1] and Register 0x00[6],

it takes effect immediately. In multibyte transfers, subsequent

bytes reflect any changes in the serial port configuration.

When MSB first mode is active, the instruction and data bytes

must be written from MSB to LSB. Multibyte data transfers in

MSB first format start with an instruction byte that includes the

data bytes must follow in order from the high address to the low

address. In MSB first mode, the serial control port internal

address generator decrements for each data byte of the multi-

byte transfer cycle.

When LSB first mode is active, the instruction and data bytes

must be written from LSB to MSB. Multibyte data transfers in

LSB first format start with an instruction byte that includes the

multiple data bytes. The internal byte address generator of the

serial control port increments for each byte of the multibyte

transfer cycle.

The AD9789 serial control port register address decrements

from the register address just written toward 0x00 for multibyte

I/O operations if the MSB first mode is active (default). If the

LSB first mode is active, the register address of the serial control

port increments from the address just written toward 0x55 for

multibyte I/O operations.

Streaming mode always terminates when it reaches Address 0x2F.

Note that unused addresses are not skipped during multibyte I/O

operations.

Table 8. Streaming Mode (No Addresses Are Skipped)

Write Mode

Address Direction

Stop Sequence

LSB First

Increment

0x02D, 0x02E, 0x02F, stop

MSB First

Decrement

0x001, 0x000, 0x02F, stop

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