AD9520-2SLASHPCBZ datasheet(55/84 Pages) AD

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AD9520-2

Rev. 0 | Page 55 of 84

SPI MSB/LSB FIRST TRANSFERS

The default mode of the AD9520 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 AD9520 to unidirectional mode (0x000[7] = 1 and

0x000[0] = 1). In unidirectional mode, the readback data

appears on the SDO pin.

The AD9520 instruction word and byte data can be MSB first

or LSB first. Any data written to 0x000 must be mirrored; the

upper four bits ([7:4]) must mirror the lower four 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 0x000, which mirrors Bit 4 and Bit 3. This sets the long

instruction mode, which is the default and the only mode

supported.

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 62).

Readback of the buffer or active registers is controlled by 0x004[0].

The AD9520 uses Register Address 0x000 to Register Address 0xB03.

The default for the AD9520 is MSB first.

SERIAL

CONTROL

PORT

UPDATE

REGISTERS

WRITE REGISTER 0x232 = 0x001

TO UPDATE REGISTERS

SCLK/SCL

SDO

SDIO/SDA

When LSB first is set by 0x000[1] and 0x000[6], it takes effect

immediately because it only affects 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.

Figure 62. Relationship Between Serial Control Port Buffer Registers and

Active Registers of the AD9520

SPI 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.

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. In a multibyte transfer cycle, the internal byte

address generator of the serial port increments for each byte.

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

bytes of data indicated by Bits[W1:W0], see Table 43.

Table 43. Byte Transfer Count

The AD9520 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 0x232 for

multibyte I/O operations.

Bytes to Transfer

Streaming mode always terminates when it reaches 0x232. Note

that unused addresses are not skipped during multibyte I/O

operations.

Table 44. Streaming Mode (No Addresses Are Skipped)

Write Mode

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

communications cycle. Only Bits[A9:A0] are needed to cover

the range of the 0x232 registers used by the AD9520. Bits[A12:A10]

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

starting byte address. In MSB first mode, subsequent bytes

increment the address.

Address Direction

Stop Sequence

LSB first

Increment

0x230, 0x231, 0x232, stop

MSB first

Decrement

0x001, 0x000, 0x232, stop

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