Analog Devices AD9865 Manual page 22

AD9865
INSTRUCTION CYCLE
SEN
SCLK
SDATA R/W N1 N2 A4 A3
A2 A1
INSTRUCTION CYCLE
SEN
SCLK
SDATA
A2 A4
A0 A1 A3 N2 N1
Figure 45. SPI Timing, MSB First (Upper), and LSB First (Lower)
When the SPI LSB first bit is set high, the serial port interprets
both instruction and data bytes LSB first. Multibyte data trans-
fers in LSB format can be completed by writing an instruction
byte that includes the register address of the first address to be
accessed. The AD9865 automatically increments the address for
each successive byte required for the multibyte communication
cycle.
Figure 46 illustrates the timing requirements for a write opera-
tion to the SPI port. After the serial port enable ( SEN ) signal
goes low, data (SDIO) pertaining to the instruction header is
read on the rising edges of the clock (SCLK). To initiate a write
operation, the read/not-write bit is set low. After the instruction
header is read, the eight data bits pertaining to the specified
register are shifted into the SDIO pin on the rising edge of the
next eight clock cycles. If a multibyte communication cycle is
specified, the destination address is decremented (MSB first)
and shifts in another eight bits of data. This process repeats until
all the bytes specified in the instruction header (N1, N0 bits) are
shifted into the SDIO pin. SEN must remain low during the data
transfer operation, only going high after the last bit is shifted
into the SDIO pin.
t f
1/
S SCLK
SEN
t t
HI LOW
SCLK
t
DS
t
DH
N1 N0
SDIO R/W
Figure 46. SPI Write Operation Timing
DATA TRANSFER CYCLE
D1 N D0 N
A0 D7 1 D6 1
DATA TRANSFER CYCLE
D6 N D7 N
R/W
D0 1 D1 1
t
H
A0 D7 D6 D1 D0
Rev. A | Page 22 of 48
Figure 47 illustrates the timing for a 3-wire read operation to
the SPI port. After SEN goes low, data (SDIO) pertaining to the
instruction header is read on the rising edges of SCLK. A read
operation occurs, if the read/not-write indicator is set high.
After the address bits of the instruction header are read, the
eight data bits pertaining to the specified register are shifted out
of the SDIO pin on the falling edges of the next eight clock cycles.
If a multibyte communication cycle is specified in the instruction
header, a similar process as previously described for a multibyte
SPI write operation applies. The SDO pin remains three-stated
in a 3-wire read operation.
t
f
1/
S
SCLK
SEN
t
t
LOW
HI
SCLK
t
DS
t
DH
N1 A2 A1
SDIO R/W
Figure 47. SPI 3-Wire Read Operation Timing
Figure 48 illustrates the timing for a 4-wire read operation to
the SPI port. The timing is similar to the 3-wire read operation
with the exception that data appears at the SDO pin, while the
SDIO pin remains high impedance throughout the operation.
The SDO pin is an active output only during the data transfer
phase and remains three-stated at all other times.
t
f
1/
S
SCLK
SEN
t t
HI LOW
SCLK
t
DS
t
DH
N1 A2 A1
SDIO R/W
SDO
Figure 48. SPI 4-Wire Read Operation Timing
t
DV
t
EZ
A0 D7 D6 D1 D0
t
EZ
A0
t
t
EZ
DV
D7 D6 D1 D0