AD9518-2ABCPZ datasheet(41/64 Pages) AD

41 / 64 page

Data Sheet

AD9518-2

Rev. C | Page 41 of 64

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 [W1:W0].

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 AD9518 serial control port is the

bidirectional mode. In bidirectional mode, both the sent data

and the readback data appear on the SDIO pin. It is also possible to

set the AD9518 to unidirectional mode via the SDO active bit,

data appears on the SDO pin.

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

port buffer area, or the data that is in the active registers (see

Figure 45). Readback of the buffer or active registers is controlled

by Register 0x004[0].

The AD9518 supports only the long instruction mode; therefore,

bits.) Long instruction mode is the default at power-up or reset.

The AD9518 uses Register Address 0x000 to Register

Address 0x232.

SCLK

SDIO

SDO

SERIAL

CONTROL

PORT

UPDATE

REGISTERS

WRITE REGISTER 0x232 = 0x01

TO UDATE REGISTERS

Figure 45. Relationship Between Serial Control Port Buffer Registers and

Active Registers of the AD9518

THE 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,

[W1:W0], indicate the length of the transfer in bytes. The final

13 bits are the address ([A12:A0]) 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[W1:W0] (see Table 37).

Table 37. Byte Transfer Count

Bytes to Transfer

Streaming mode

The 13 bits found in [A12:A0] select the address within the

transfer portion of the communications cycle. Only Bits[A9:A0]

are needed to cover the range of the 0x232 registers used by the

AD9518. Bits[A12:A10] must always be set to 0b. For multibyte

transfers, this address is the starting byte address. In MSB first

mode, subsequent bytes decrement the address.

MSB/LSB FIRST TRANSFERS

The AD9518 instruction word and byte data can be MSB first

or LSB first. Any data written to Register 0x000 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, see the default setting

for this register: 0x18, which mirrors Bit 4 and Bit 3. This sets

the long instruction mode (which is the default and the only

mode that is supported).

The default for the AD9518 is MSB first.

When LSB first is set by Register 0x000[1] and Register 0x000[6],

it takes effect immediately because it affects only the operation

of the serial control port and does not require that an update be

executed.

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

multibyte transfer cycle.

When LSB first 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 register

address of the least significant data byte followed by multiple

data bytes. The internal byte address generator of the serial

control port increments for each byte of the multibyte

transfer cycle.

The AD9518 serial control port register address decrements

from the register address just written toward 0x000 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 Register

Address 0x232 for multibyte I/O operations.

Streaming mode always terminates when it hits Address 0x232.

Note that unused addresses are not skipped during multibyte

I/O operations.

Table 38. Streaming Mode (No Addresses Are Skipped)

Write Mode

Address Direction

Stop Sequence

LSB first

Increment

0x230, 0x231, 0x232, stop

MSB first

Decrement

0x001, 0x000, 0x232, stop

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