AD5665-RBRUZ-2 datasheet(24/32 Pages) AD

24 / 32 page

AD5625R/AD5645R/AD5665R, AD5625/AD5665

Preliminary Technical Data

Rev. PrA. | Page 24 of 32

MULTIPLE BYTE WRITE

Once an AD56x5 has been addressed, one or more three-byte

blocks of command and data can be sent to the device, until a

stop condition is received. The device must then be re-

addressed. For this type of operation, the “S” bit in the

command byte is set to zero.

For some types of application such as waveform generation, it

may be required to update a DAC or DACs as fast as possible

without changing the command byte. In this case the “S” bit in

the initial command byte is set to 1. This sets the command

parameters for all subsequent data. Thereafter, multiple two-

byte blocks of data high byte and data low byte can be sent,

without sending a further command byte, until a stop condition

is received.

The “S” bit is only active in the first command byte following

the device slave address. Therefore, even if the “S” bit is 0 and

three-byte blocks of command and data are being sent, it is not

possible to alter the multi-byte mode by changing the “S” bit to

1 “on-the-fly” during any subsequent command byte.

STOP

LEAST SIGNIFICANT

DATA BYTE

MOST SIGNIFICANT

DATA BYTE

COMMAND

BYTE

BLOCK 1

S=0

SLAVE

ADDRESS

LEAST SIGNIFICANT

DATA BYTE

MOST SIGNIFICANT

DATA BYTE

COMMAND

BYTE

BLOCK 2

S=0

LEAST SIGNIFICANT

DATA BYTE

MOST SIGNIFICANT

DATA BYTE

COMMAND

BYTE

BLOCK n

S=0

Figure 57. Multiple Block Write With Command Byte in Each Block (S=0)

STOP

LEAST SIGNIFICANT

DATA BYTE

MOST SIGNIFICANT

DATA BYTE

COMMAND

BYTE

BLOCK 1

S=1

SLAVE

ADDRESS

LEAST SIGNIFICANT

DATA BYTE

MOST SIGNIFICANT

DATA BYTE

BLOCK 2

S=1

LEAST SIGNIFICANT

DATA BYTE

MOST SIGNIFICANT

DATA BYTE

BLOCK n

S=1

Figure 58. Multiple Block Write With Initial Command Byte Only (S=1)

BROADCAST MODE

In addition to the unique slave address for each device, which is

set by the address pin(s), The AD56x5 has a broadcast address

to which any AD56x5 will respond, irrespective of the state of

the address pin(s). This address is 0001000(Write). Where

several AD56x5 devices are connected to a bus, they can all be

sent the same data using the broadcast address. The broadcast

address only works for write operations. It is not possible to

read back data from several devices at the same time, due to bus

contention.

INPUT SHIFT REGISTER

The input shift register is 24 bits wide to store the 3 data bytes

written to the device of the serial interface. Data written to the

device is split into four sections:

- One bit to select multiple byte operation.

- a three bit command that tells the device what operation to

perform.

- a three-bit address that tells the device to which DAC or

DACs the command applies.

- 16 bits of data, which, depending on the command may be

written to a DAC or used to define the parameters of a

command operation.

Bit 23 of the input shift register is reserved, and should always

be set to 0 when writing to the device.

The command and address are contained in the command byte,

the 8 MSBs of the input register. The middle 8 bits are the high

byte of the DAC data, while the 8 least significant bits are the

low byte of the DAC data or command data. DAC data is left

justified, so the two LSBs are unused for the 14 bit AD5645R,

and the four LSBs are unused for the 12-bit AD5625R (but they

are still used for command data in these devices.

The AD56x5 has seven different commands that can be written

to it.

D15

D14

D13

D12

D11

D10

COMMAND

DAC ADDRESS

DAC DATA

DAC OR COMMAND DATA

COMMAND BYTE

DATA HIGH BYTE

DATA LOW BYTE

DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10

DB9

DB8

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

Figure 59. AD5665R/AD5665 Input Shift Register (16-Bit DAC)

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