AD9860_15 Datasheet, PDF (17/32 Pages) Analog Devices – Mixed-Signal Front-End Processor for Broadband Communications

AD9860/AD9862
Blank Registers
Blank registers, i.e., the registers with 0 settings and no indicated
function, are placeholders used throughout the register map for
spacing the AD9860/AD9862 control bits in a logic fashion and,
potentially can be used for future development. A low should
always be written to these registers if a write needs to take place.
SERIAL PORT INTERFACE
The Serial Port Interface (SPI) is used to write to and read from
the AD9860/AD9862 internal programmable registers. The serial
interface uses four pins: SEN, SCLK, SDIO, and SDO by default.
SEN is a serial port enable pin, SCLK is the serial clock pin,
SDIO is a bidirectional data line and SDO is a serial output pin.
SEN is an active low control gating read and write cycles. When
SEN is high, SDO and SDIO are three-stated.
SCLK is used to synchronize SPI read and writes at a maximum
bit rate of 16 MHz. Input data is registered on the rising edge and
output data transitions on the falling edge. During write opera-
tions, the registers are updated after the 16th rising clock edge
(and 24th rising clock edge for the dual byte case). Incomplete
write operations are ignored.
SDIO is an input only by default. Optionally, a 3-pin interface may
be configured using the SDIO for both input and output opera-
tions and three-stating the SDO pin (see SDIO BiDir register).
t_S
SEN
SCLK ^{DON’T CARE}
t_DH
t_DS
t_LO
t_HI
t_CLK
SDO is a serial output pin used for read back operations in 4-wire mode
and is three-stated when SDIO is configured for bidirectional operation.
Instruction Header
Each SPI read or write consists of an instruction header and
data. The instruction header is made up of an 8-bit word and is
used to set up the register data transfer. The 8-bit word consists
of a read/not write bit, R/nW (the MSB), followed by a double/
not single bit (2/n1) and the 6-bit register address.
Write Operations
The SPI write operation uses the instruction header to configure
a one or two register write using the 2/n1 bit. The instruction
byte followed by the register data, is written serially into the
device through the SDIO pin on rising edges of the interface
clock at SCLK. The data can be transferred MSB first or LSB first
depending on the setting of the LSB First register.
Figure 1 includes a few examples of writing data into the device.
Figure 1a shows a write using 1 Byte and MSB First mode set;
Figure 1b shows an MSB first, 2 Byte write; and Figure 1c
shows an LSB first, 2 Byte write. Note the differences between
LSB and MSB First modes: instruction header and data are
reversed, and in 2 Byte writes, the first data byte is written to
the address in the header, N and the second data byte is written
to the n–1 address. In LSB First mode, the first data byte is still
written to the address in the instruction header, but the second
data byte is written to the N+1 address.
t_H
DON’T CARE
SDIO
DON’T CARE R/nW 2/n1 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 DON’T CARE
INSTRUCTION HEADER
REGISTER DATA
t_DH
t_LO
t_CLK
t_S
t_H
t_DS
t_HI
SEN
SCLK ^{DON’T CARE}
DON’T CARE
SDIO ^{DON’T CARE R/nW 2/n1 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0 DON’T CARE}
INSTRUCTION HEADER (REGISTER N)
REGISTER (N) DATA
REGISTER (N–1) DATA
SEN
SCLK
t_DH
t_LO
t_CLK
t_S
t_DS
t_HI
t_H
DON’T CARE
SDIO
A0 A1 A2 A3 A4 A5 2/n1 R/nW D0 D1 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5 D6 D7 DON’T CARE
INSTRUCTION HEADER (REGISTER N)
REGISTER (N) DATA
REGISTER (N+1) DATA
Figure 1. SPI Write Examples a. (top) 1 Byte, MSB First Mode; b. (middle) 2 Byte, MSB First Mode;
c. (bottom) 2 Byte, LSB First Mode
REV. 0
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