
REV. 0
AD9875
–20–
Figures 10a and 10b show how the serial port words are built
for each of these modes.
SENABLE
SCLK
SDATA
R/WI6
(N)
I5
(N)
I3
I4
I2
I1
I0
D7
N
D6
N
D2
0
D1
0
D0
0
INSTRUCTION CYCLE
DATA TRANSFER CYCLE
Figure 10a. Serial Register Interface Timing MSB-First
SENABLE
SCLK
SDATA
I0
I6
(N)
I5
(N)
I3
I4
I2
I1
R/W
D7
N
D6
N
D2
0
D1
0
D0
0
INSTRUCTION CYCLE
DATA TRANSFER CYCLE
Figure 10b. Serial Register Interface Timing LSB-First
Notes on Serial Port Operation
T he serial port is disabled and all registers are set to their default
values during a hardware reset. During a software reset, all
registers except register 0 are set to their default values. Register
0 will remain at the last value sent, with the exception that the
Software Reset
bit will be set to 0.
T he serial port is operated by an internal state machine and is
dependent on the number of SCLK cycles since the last time
SENABLE
went active. On every eighth rising edge of SCLK , a
byte is transferred over the SPI. During a multibyte write cycle,
this means the registers of the AD9875 are not simultaneously
updated, but occur sequentially. For this reason, it is recom-
mended that single byte transfers be used when changing the
SPI configuration or performing a software reset.
T able IV. Register Layout
Address
(hex)
Default
(hex)
0
×
00
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Comments
0
SPI
LSB First
Software
Reset
Read/Write
1
Power-
Down
Regulator
Power-
Down
PLL-B
Power-
Down
PLL-A
Power-
Down
DAC
Power-
Down
Interpolator
Power-
Down
Rx
Reference
Power-
Down
ADC and
FPGA
Power-
Down
Rx LPF and
CPGA
0
×
00
Read/Write
PWR DN
Pin Low
2
Power-
Down
Regulator
Power-
Down
PLL-B
Power-
Down
PLL-A
Power-
Down
DAC
Power-
Down
Interpolator
Power-
Down
Rx
Reference
Power-
Down
ADC and
FPGA
Power-
Down
Rx LPF and
CPGA
0
×
9F
Read/Write
PWR DN
Pin High
3
T x Port
Negative
Edge
Sampling
ADC Clock
Source
PLL-B/2
PLL-B
(
×
M) Multiplier
< 5:4>
PLL-B
(
) Divider
< 3:3>
PLL-A
(
×
M) Multiplier
< 1:0>
0
×
02
Read/Write
4
T x Port
T uning
Update
Disable
Rx LPF
T uning
In Progress
(Read Only)
Rx Path
DC Offset
Correction Bypass
Rx Digital Fast ADC
HPF
Wideband
Rx LPF
Enable
1-Pole
Rx LPF
Rx LPF
Bypass
0
×
01
Read/Write
Sampling
5
Rx LPF Fc Adjust <4:0>
0
×
80
0
×
00
Read/Write
6
PGA
Gain Set
by Register
Rx Path Gain Adjust <4:0>
Read/Write
7
Interpolation Filter Select
<3:0>
Power-Down
Interpolator
at
T x QUIET
Pin Low
T x Port
LS Nibble
First
T x Port
Width
5-bits
T x Port
Multiplexer
Bypass
0
×
00
Read/Write
8
Invert
CLK B
Invert
CLK B
Invert
CLK B
Invert
CLK B
T hree-State
Rx Port
Rx Port
LS Nibble
First
Rx Port
Width
5-bits
Rx Port
Multiplexer
Bypass
0
×
00
Read/ Write
F
Die Revision Number <3:0>
Read Only