Datasheet

AD9832 Data Sheet
Rev. E | Page 16 of 28
Table 11. Writing to the AD9832 Data Registers
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
C3 C2 C1 C0 A3 A2 A1 A0 MSB X
1
X
1
X
1
X
1
X
1
X
1
LSB
1
X = don’t care.
Table 12. Setting SYNC and SELSRC
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
1 0 SYNC SELSRC X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
1
X = don’t care.
Table 13. Power-Down, Resetting and Clearing the AD9832
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
1 1 SLEEP RESET CLR X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
X
1
1
X = don’t care.
LATENCY
Associated with each operation is a latency. When inputs
FSELECT/PSEL change value, there is a pipeline delay before
control is transferred to the selected register; there is a pipeline
delay before the analog output is controlled by the selected
register. When times t
11
and t
11A
are met, PSEL0, PSEL1, and
FSELECT have latencies of six MCLK cycles when SYNC = 0.
When SYNC = 1, the latency is increased to 8 MCLK cycles.
When times t
11
and t
11A
are not met, the latency can increase by
one MCLK cycle. Similarly, there is a latency associated with
each write operation. If a selected frequency/phase register is
loaded with a new word, there is a delay of 6 to 7 MCLK cycles
before the analog output will change (there is an uncertainty of
one MCLK cycle regarding the MCLK rising edge at which the
data is loaded into the destination register). When SYNC = 1,
the latency is 8 or 9 MCLK cycles.
FLOWCHARTS
The flowchart in Figure 24 shows the operating routine for the
AD9832. When the AD9832 is powered up, the part should be
reset, which resets the phase accumulator to zero so that the
analog output is at full scale. To avoid spurious DAC outputs
while the AD9832 is being initialized, the RESET bit should be
set to 1 until the part is ready to begin generating an output.
Taking CLR high sets SYNC and SELSRC to 0 so that the
FSELECT/PSELx pins are used to select the frequency/phase
registers, and the synchronization circuitry is bypassed. A write
operation is needed to the SYNC/SELSRC register to enable the
synchronization circuitry or to change control to the FSELECT/
PSEL bits. RESET does not reset the phase and frequency registers.
These registers will contain invalid data and, therefore, should
be set to a known value by the user. The RESET bit is then set to 0
to begin generating an output. A signal will appear at the DAC
output 6 MCLK cycles after RESET is set to 0.
The analog output is f
MCLK
/2
32
× FREG, where FREG is the value
loaded into the selected frequency register. This signal is phase
shifted by the amount specified in the selected phase register
(2π/4096 × PHASEx REG, where PHASEx REG is the value
contained in the selected phase register).
Control of the frequency/phase registers can be interchanged
from the pins to the bits.