AD9783 Analog Devices, AD9783 Datasheet - Page 18

• Manufacturer Part Number: AD9783
• Description: Dual 16-Bit, LVDS Interface 500 MSPS DAC
• Manufacturer: Analog Devices

Specifications of AD9783

• Resolution (bits): 16bit
• Dac Update Rate: 500MSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): +3.47V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: LVDS,Par

AD9780/AD9781/AD9783
THEORY OF OPERATION
The AD9780/AD9781/AD9783 have a combination of features
that make them very attractive for wired and wireless commu-
nications systems. The dual DAC architecture facilitates easy
interface to common quadrature modulators when designing
single sideband transmitters. In addition, the speed and
performance of the devices allow wider bandwidths and more
carriers to be synthesized than in previously available products.
All features and options are software programmable through
the SPI port.
SERIAL PERIPHERAL INTERFACE
The serial peripheral interface (SPI) port is a flexible, synchron-
ous serial communications port allowing easy interface to many
industry-standard microcontrollers and microprocessors. The
port is compatible with most synchronous transfer formats,
including both the Motorola SPI and Intel
The interface allows read and write access to all registers that
configure the AD9780/AD9781/AD9783. Single or multiple
byte transfers are supported as well as MSB-first or LSB-first
transfer formats. Serial data input/output can be accomplished
through a single bidirectional pin (SDIO) or through two
unidirectional pins (SDIO/SDO).
The serial port configuration is controlled by Register 0x00,
Bits[7:6]. It is important to note that any change made to the
serial port configuration occurs immediately upon writing to
the last bit of this byte. Therefore, it is possible with a multibyte
transfer to write to this register and change the configuration in
the middle of a communication cycle. Care must be taken to
compensate for the new configuration within the remaining
bytes of the current communication cycle.
Use of a single-byte transfer when changing the serial port
configuration is recommended to prevent unexpected device
behavior.
GENERAL OPERATION OF THE SERIAL INTERFACE
There are two phases to any communication cycle with the
AD9780/AD9781/AD9783: Phase 1 and Phase 2. Phase 1 is
the instruction cycle, which writes an instruction byte into
the device. This byte provides the serial port controller with
information regarding Phase 2 of the communication cycle:
the data transfer cycle.
SCLK
SDIO
SDO
CSB
Figure 51. SPI Port
AD9783
PORT
SPI
®
SSR protocols.
Rev. A | Page 18 of 36
The Phase 1 instruction byte defines whether the upcoming
data transfer is a read or write, the number of bytes in the data
transfer, and a reference register address for the first byte of the
data transfer. A logic high on the CSB pin followed by a logic
low resets the SPI port to its initial state and defines the start of
the instruction cycle. From this point, the next eight rising
SCLK edges define the eight bits of the instruction byte for the
current communication cycle.
The remaining SCLK edges are for Phase 2 of the communication
cycle, which is the data transfer between the serial port controller
and the system controller. Phase 2 can be a transfer of one, two,
three, or four data bytes as determined by the instruction byte.
Using multibyte transfers is usually preferred, although single-
byte data transfers are useful to reduce CPU overhead or when
only a single register access is required.
All serial port data is transferred to and from the device in
synchronization with the SCLK pin. Input data is always latched
on the rising edge of SCLK, whereas output data is always valid
after the falling edge of SCLK. Register contents change imme-
diately upon writing to the last bit of each transfer byte.
Anytime synchronization is lost, the device has the ability to
asynchronously terminate an I/O operation whenever the CSB pin
is taken to logic high. Any unwritten register content data is lost
if the I/O operation is aborted. Taking CSB low then resets the
serial port controller and restarts the communication cycle.
INSTRUCTION BYTE
The instruction byte contains the information shown in Table 9.
Table 9.
MSB
B7
R/W
Bit 7, R/W, determines whether a read or a write data transfer
occurs after the instruction byte write. Logic 1 indicates a read
operation. Logic 0 indicates a write operation.
Bits[6:5], N1 and N0, determine the number of bytes to be
transferred during the data transfer cycle. The bits decode as
shown in Table 10.
Table 10. Byte Transfer Count
N1
0
0
1
1
B6
N1
N0
0
1
0
1
B5
N0
Description
Transfer one byte
Transfer two bytes
Transfer three bytes
Transfer four bytes
B4
A4
B3
A3
B2
A2
B1
A1
LSB
B0
A0