Datasheet

Data Sheet AD9833
Rev. G | Page 13 of 21
FUNCTIONAL DESCRIPTION
SERIAL INTERFACE
The AD9833 has a standard 3-wire serial interface that is
compatible with the SPI, QSPI™, MICROWIRE®, and DSP
interface standards.
Data is loaded into the device as a 16-bit word under the
control of a serial clock input, SCLK. The timing diagram for
this operation is given in Figure 4.
The FSYNC input is a level-triggered input that acts as a frame
synchronization and chip enable. Data can be transferred into the
device only when FSYNC is low. To start the serial data transfer,
FSYNC should be taken low, observing the minimum FSYNC-
to-SCLK falling edge setup time, t
7
. After FSYNC goes low, serial
data is shifted into the input shift register of the device on the
falling edges of SCLK for 16 clock pulses. FSYNC may be taken
high after the 16th falling edge of SCLK, observing the minimum
SCLK falling edge to FSYNC rising edge time, t
8
. Alternatively,
FSYNC can be kept low for a multiple of 16 SCLK pulses and
then brought high at the end of the data transfer. In this way, a
continuous stream of 16-bit words can be loaded while FSYNC
is held low; FSYNC goes high only after the 16th SCLK falling
edge of the last word loaded.
The SCLK can be continuous, or it can idle high or low between
write operations. In either case, it must be high when FSYNC
goes low (t
11
).
For an example of how to program the AD9833, see the AN-1070
Application Note on the Analog Devices, Inc., website.
POWERING UP THE AD9833
The flowchart in Figure 26 shows the operating routine for the
AD9833. When the AD9833 is powered up, the part should be
reset. This resets the appropriate internal registers to 0 to provide
an analog output of midscale.
To avoid spurious DAC outputs during AD9833 initialization,
the reset bit should be set to 1 until the part is ready to begin
generating an output. A reset does not reset the phase, frequency,
or control registers. These registers will contain invalid data and,
therefore, should be set to known values by the user. The reset
bit should then be set to 0 to begin generating an output. The
data appears on the DAC output seven or eight MCLK cycles
after the reset bit is set to 0.
LATENCY PERIOD
A latency period is associated with each asynchronous write
operation in the AD9833. If a selected frequency or phase
register is loaded with a new word, there is a delay of seven
or eight MCLK cycles before the analog output changes. The
delay can be seven or eight cycles, depending on the position
of the MCLK rising edge when the data is loaded into the
destination register.
CONTROL REGISTER
The AD9833 contains a 16-bit control register that allows the
user to configure the operation of the AD9833. All control bits
other than the mode bit are sampled on the internal falling edge
of MCLK.
Table 6 describes the individual bits of the control register.
The different functions and the various output options of
the AD9833 are described in more detail in the Frequency and
Phase Registers section.
To inform the AD9833 that the contents of the control register
will be altered, D15 and D14 must be set to 0, as shown in Table 5.
Table 5. Control Register Bits
D15 D14 D13 D0
0 0 Control Bits
SIN
ROM
PHASE
ACCUMULATOR
(28-BIT)
AD9833
(LOW POWER)
10-BIT DAC
0
MUX
1
SLEEP12
SLEEP1
RESET
MODE + OPBITEN
DIV2
OPBITEN
VOUT
1
MUX
0
DIGITAL
OUTPUT
(ENABLE)
DIVIDE
BY 2
DB15
0
DB14
0
DB13
B28
DB12
HLB
DB11
FSELECT
DB10
PSELECT
DB9
0
DB8
RESET
DB7
SLEEP1
DB6
SLEEP12
DB5
OPBITEN
DB4
0
DB3
DIV2
DB2
0
DB1
MODE
DB0
0
02704-024
Figure 24. Function of Control Bits