Data Sheet
AD9737A/AD9739A
Rev. | Page 41 of 64
significant bit (MSB) first and least significant bit (LSB) first
data formats
. Figure 153 illustrates how the serial port words
are formed for the MSB first and LSB first modes. The bit order
is controlled by the LSB/MSB bit (Register 0x00, Bit 6). The
default value of Bit 6 is 0, MSB first. When the LSB/MSB bit is
set high, the serial port interprets both instruction and data bytes
LSB first.
SCLK
SDATA
SCLK
SDATA
R/W
A1
A3
A2
A4
N1
N2
A0
A3
A1
A2
A0
A4
D71
D01 D11
D6N D7N
D61
D1N D0N
DATA TRANSFER CYCLE
INSTRUCTION CYCLE
DATA TRANSFER CYCLE
INSTRUCTION CYCLE
09616-
073
CS
Figure 153. SPI Timing, MSB First (Upper) and LSB First (Lower)
operation to the SPI port. After the serial port enable (CS)
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.
the SPI port. After CS 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.
the SPI port. The timing is similar to the 3-wire read operation
with the exception that data appears at the SDO pin only, whereas
the SDIO pin remains at 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.
D7
D6
A0
D1
N1
N0
tS
SCLK
SDIO
1/
fSCLK
tLOW
tHI
tDS
tDH
R/W
D0
tH
09616-
074
CS
Figure 154. SPI Write Operation Timing
D7
D6
A0
D1
N1
tS
SCLK
SDIO
1/
fSCLK
tLOW
tHI
tDS
tDH
R/W
D0
tEZ
A2
A1
tDV
09616-
075
CS
Figure 155. SPI 3-Wire Read Operation Timing
A0
CS
N1
tS
SCLK
SDIO
1/
fSCLK
tLOW
tHI
tDS
tDH
R/W
tEZ
A2
A1
tDV
D7
D6
D1
SDO
D0
tEZ
09616-
076
Figure 156. SPI 4-Wire Read Operation Timing
C