Datasheet

AD9148 Data Sheet
Rev. B | Page 40 of 72
INPUT DATA PORTS
The AD9148 can operate in three data input modes: dual-port
mode, single-port mode, and byte mode. In dual-port mode,
DAC 1 and DAC 2 receive data from Port A, and DAC 3 and
DAC 4 receive data from Port B. In single-port mode, all four
DACs receive data from Port A. In byte mode, all four DACs
receive data from Port A, but the port is split into two 8-bit wide
buses. In all modes, the data input timing is relative to a DCI signal
provided with the data.
DUAL-PORT MODE
In dual-port mode, the DCI signal indicates to which DAC the
data is intended. On the rising edge of DCI, data is latched into
DAC 1 and DAC 3. On the falling edge of DCI, data is latched
into DAC 2 and DAC 4. This pattern repeats continuously.
There is a SPI programmable option (Register 0x14[6]) to provide
one DCI for both input ports or two DCIs, where each DCI is
associated with one input port. Two DCIs are useful when the
data for each port is coming from a different data source. These
cases are illustrated in Figure 45 and Figure 46.
DCIA
A[15:0]
DAC1 DAC2 DAC1 DAC2 DAC1 DAC2 DAC1 DAC2
DAC3 DAC4 DAC3 DAC4 DAC3 DAC4 DAC3 DAC4
B[15:0]
08910-045
Figure 45. Timing Diagram for Dual-Port Mode, One DCI
DCIA
A[15:0]
DAC1 DAC2 DAC1 DAC2 DAC1 DAC2 DAC1 DAC2
DAC3 DAC4 DAC3 DAC4 DAC3 DAC4 DAC3 DAC4
B[15:0]
DCIB
08910-046
Figure 46. Timing Diagram for Dual-Port Mode, Two DCI
Each data sample, by default, is expected to be formatted as an
MSB sent to Bit 15 and an LSB sent to Bit 0 for each port. The
AD9148 contains an option to swap the bus (Register 0x03[4]).
When this bus swap bit is set, the MSB should be sent to Bit 0,
and the LSB should be sent to Bit 15 for each port.
SINGLE-PORT MODE
In single-port mode, a FRAME signal must be provided along
with the DCI signal and the data. The FRAME signal indicates
to which DAC the data is intended. When FRAME goes high,
the first data-word goes to DAC 1, and the second data-word
goes to DAC 2. When FRAME goes low, the first data-word
goes to DAC 3, and the second data-word goes to DAC 4.
This pattern repeats continuously as illustrated in Figure 47.
FRAMEA
A[15:0]
DAC1 DAC2 DAC3 DAC4 DAC1 DAC2 DAC3 DAC4
DCIA
08910-047
Figure 47. Timing Diagram for Single-Port Mode
Each data sample, by default, is expected to be formatted as an MSB
sent to Bit 15 and an LSB sent to Bit 0. When the bus swap bit is
set (Register 0x03[4]), the MSB should be sent to Bit 0, and the
LSB should be sent to Bit 15 for each port.
The FRAME signal is sampled with the same internal signal as
the data and has the same set-up and hold timing relative to DCI. If
desired, only the first FRAME pulse needs to be generated. This
initializes the internal clock phases inside the device, and data
latches just as if the periodic FRAME signal were sent.