AD9865
INSTRUCTION CYCLE
DATA TRANSFER CYCLE
Figure 47 illustrates the timing for a 3-wire read operation to
the SPI port. After goes low, data (SDIO) pertaining to the
SEN
SEN
SCLK
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.
R/W
N1 N2
A4 A3
D1
D0
A1 A0
D7 D6
1 1
A2
SDATA
N
N
INSTRUCTION CYCLE
DATA TRANSFER CYCLE
SEN
SCLK
D6 D7
N
A2
A4
A0
A1
N2
A3
N1
R/W
SDATA
N
D0 D1
1
1
tS
1/fSCLK
Figure 45. SPI Timing, MSB First (Upper), and LSB First (Lower)
SEN
tLOW
tHI
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.
SCLK
tDV
tDS
tDH
tEZ
A1
A0
D6 D1 D0
N1
D7
A2
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.
Figure 46 illustrates the timing requirements for a write opera-
tion to the SPI port. After the serial port enable (
) signal
SEN
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
tS
1/fSCLK
SEN
tLOW
tHI
SCLK
tDS
tDH
tEZ
tEZ
A1
A0
N1
A2
SDIO
SDO
R/W
tDV
shifted into the SDIO pin.
must remain low during the data
SEN
D7 D6 D1 D0
transfer operation, only going high after the last bit is shifted
into the SDIO pin.
Figure 48. SPI 4-Wire Read Operation Timing
tS
1/fSCLK
tH
SEN
tLOW
tHI
SCLK
tDS
tDH
N1
N0
A0
D7
D6 D1
D0
SDIO
R/W
Figure 46. SPI Write Operation Timing
Rev. A | Page 22 of 48
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