AD9779-EBZ Analog Devices Inc, AD9779-EBZ Datasheet - Page 25

• Manufacturer Part Number: AD9779-EBZ
• Description: BOARD EVALUATION FOR AD9779
• Manufacturer: Analog Devices Inc

Specifications of AD9779-EBZ

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

THEORY OF OPERATION
The AD9776/AD9778/AD9779 combine many features that
make them very attractive DACs for wired and wireless
communications systems. The dual digital signal path and
dual DAC structure allow an easy interface with common
quadrature modulators when designing single sideband
transmitters. The speed and performance of the parts allow
wider bandwidths and more carriers to be synthesized than
in previously available DACs. The digital engine uses a break-
through filter architecture that combines the interpolation with
a digital quadrature modulator. This allows the parts to conduct
digital quadrature frequency upconversion. They also have
features that allow simplified synchronization with incoming
data and between multiple parts.
The serial port configuration is controlled by Register 0x00,
Bits<6:7>. It is important to note that the configuration changes
immediately upon writing to the last bit of the byte. For multi-
byte transfers, writing to this register can occur during the
middle of a communication cycle. Care must be taken to
compensate for this new configuration for the remaining bytes
of the current communication cycle.
The same considerations apply to setting the software reset,
RESET (Register 0x00, Bit 5) or pulling the RESET pin (Pin 70)
high. All registers are set to their default values, except
Register 0x00 and Register 0x04, which remain unchanged.
Use of only single-byte transfers when changing serial port
configurations or initiating a software reset is recommended to
prevent unexpected device behavior.
As described in this section, all serial port data is transferred
to/from the device in synchronization to the SCLK pin. If
synchronization is lost, the device has the ability to asynchro-
nously terminate an I/O operation, putting the serial port
controller into a known state and, thereby, regaining
synchronization.
SERIAL PERIPHERAL INTERFACE
The serial port is a flexible, synchronous serial communications
port allowing easy interface to many industry-standard micro-
controllers and microprocessors. The serial I/O is compatible
with most synchronous transfer formats, including both the
Motorola SPI
read/write access to all registers that configure the AD9776/
AD9778/AD9779. Single or multiple byte transfers are sup-
®
and Intel
SPI_SCLK
SPI_SDO
SPI_CSB
SPI_SDI
®
Figure 52. SPI Port
SSR protocols. The interface allows
66
67
68
69
PORT
SPI
Rev. A | Page 25 of 56
ported, as well as MSB-first or LSB-first transfer formats. The
serial interface ports can be configured as a single pin I/O (SDIO)
or two unidirectional pins for input/output (SDIO/SDO).
General Operation of the Serial Interface
There are two phases to a communication cycle with the
AD977x. Phase 1 is the instruction cycle (the writing of an
instruction byte into the device), coincident with the first eight
SCLK rising edges. The instruction byte provides the serial port
controller with information regarding the data transfer cycle,
Phase 2 of the communication cycle. 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 the starting
register address for the first byte of the data transfer. The first
eight SCLK rising edges of each communication cycle are used
to write the instruction byte into the device.
A logic high on the CSB pin followed by a logic low resets the
SPI port timing to the initial state of the instruction cycle.
From this state, the next eight rising SCLK edges represent the
instruction bits of the current I/O operation, regardless of the
state of the internal registers or the other signal levels at the
inputs to the SPI port. If the SPI port is in an instruction cycle
or a data transfer cycle, none of the present data is written.
The remaining SCLK edges are for Phase 2 of the communica-
tion cycle. Phase 2 is the actual data transfer between the device
and the system controller. Phase 2 of the communication cycle
is a transfer of one, two, three, or four data bytes as determined
by the instruction byte. Using one multibyte transfer is preferred.
Single-byte data transfers are useful in reducing CPU overhead
when register access requires only one byte. Registers change
immediately upon writing to the last bit of each transfer byte.
Instruction Byte
The instruction byte contains the information shown in
Table 9.
Table 9. SPI Instruction Byte
MSB
I7
R/W
R/ W , Bit 7 of the instruction byte, determines whether a read or
a write data transfer occurs after the instruction byte write.
Logic high indicates a read operation. Logic 0 indicates a write
operation.
N1 and N0, Bit 6 and Bit 5 of the instruction byte, determine
the number of bytes to be transferred during the data transfer
cycle. The bit decodes are listed in Table 10.
A4, A3, A2, A1, and A0—Bit 4, Bit 3, Bit 2, Bit 1, and Bit 0, respec-
tively, of the instruction byte determine the register that is accessed
during the data transfer portion of the communication cycle.
I6
N1
I5
N0
AD9776/AD9778/AD9779
I4
A4
I3
A3
I2
A2
I1
A1
LSB
I0
A0