Serial Interface Port Pin Descriptions; Msb/Lsb Transfers - Analog Devices AD9776A Manual

SERIAL INTERFACE PORT PIN DESCRIPTIONS

Serial Clock (SCLK)
The serial clock pin synchronizes data to and from the device
as well as running the internal state machines. The maximum
frequency of SCLK is 40 MHz. All data input is registered on
the rising edge of SCLK. All data is driven out on the falling
edge of SCLK.
Chip Select (CSB)
Active low input starts and gates a communication cycle. It
allows more than one device to be used on the same serial
communications lines. The SDO and SDIO pins go to a high
impedance state when this input is high. Chip select should
stay low during the entire communication cycle.
Serial Data I/O (SDIO)
Data is always written into the device on this pin. However, this
pin can be used as a bidirectional data line. The configuration
of this pin is controlled by Register 0x00, Bit 7. The default is
Logic 0, configuring the SDIO pin as unidirectional.
Serial Data Out (SDO)
Data is read from this pin for protocols that use separate lines
for transmitting and receiving data. In the case where the device
operates in a single bidirectional I/O mode, this pin does not
output data and is set to a high impedance state.

MSB/LSB TRANSFERS

The serial port can support both MSB first and LSB first data
formats. This functionality is controlled by Register Bit LSB/MSB
First (Register 0x00, Bit 6). The default is MSB first (LSB/MSB
First = 0).
When LSB/MSB first = 0 (MSB first) the instruction and
data bit must be written from MSB to LSB. Multibyte data
transfers in MSB first format start with an instruction byte
that includes the register address of the most significant data
byte. Subsequent data bytes should follow from high address to
low address. In MSB first mode, the serial port internal byte address
generator decrements for each data byte of the multibyte
communication cycle.
When LSB/MSB First = 1 (LSB first) the instruction and data
bit must be written from LSB to MSB. Multibyte data transfers
in LSB first format start with an instruction byte that includes
the register address of the least significant data byte followed by
multiple data bytes. The serial port internal byte address genera-
tor increments for each byte of the multibyte communication cycle.
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The serial port controller data address decrements from the data
address written toward 0x00 for multibyte I/O operations if the
MSB first mode is active. The serial port controller address incre-
ments from the data address written toward 0x1F for multibyte
I/O operations if the LSB first mode is active.
INSTRUCTION CYCLE
CSB
SCLK
R/W N1 N0
SDIO
SDO
Figure 53. Serial Register Interface Timing, MSB First
INSTRUCTION CYCLE
CSB
SCLK
A0 A1 A2
SDIO
SDO
Figure 54. Serial Register Interface Timing, LSB First
t
DS
CSB
SCLK
t
DS
INSTRUCTION BIT 7
SDIO
Figure 55. Timing Diagram for SPI Register Write
CSB
SCLK
SDIO
DATA BIT n
SDO
Figure 56. Timing Diagram for SPI Register Read
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AD9776A/AD9778A/AD9779A
DATA TRANSFER CYCLE
A4 A3 A2 A1 A0 D7 D6 D5 D3
N N 0
D7 D6 D5 D3
N N 0
DATA TRANSFER CYCLE
A3 A4 N0 N1 R/W D0 D1 D2 D4
0 0 0 N
D0 D1 D2 D4
0 0 0 N
t
SCLK
t t
PWH PWL
t
DH
INSTRUCTION BIT 6
t
DV
DATA BIT n–1
D2 D1 D0
0 0 0
D2 D1 D0
0 0 0
D5 D6 D7
N N N
D5 D6 D7
N N N