AD9957 Analog Devices, AD9957 Datasheet - Page 21

• Manufacturer Part Number: AD9957
• Description: 1 GSPS Quadrature Digital Upconverter
• Manufacturer: Analog Devices

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DataSheet
4
PRELIMINARY TECHNICAL DATA
SERIAL PROGRAMMING
CONTROL INTERFACE—SERIAL I/O
The AD9957 serial port is a flexible, synchronous serial communi-
cations port allowing easy interface to many industry standard
microcontrollers and microprocessors. The serial I/O is compatible
with most synchronous transfer formats, including both the Mo-
torola 6905/11 SPI and Intel 8051 SSR protocols.
The interface allows read/write access to all registers that configure
the AD9957. MSB first or LSB first transfer formats are supported.
In addition, the AD9957’s serial interface port can be configured as
a single pin I/O (SDIO), which allows a two-wire interface or two
unidirectional pins for in/out (SDIO/SDO), which enables a three
wire interface. Two optional pins (IORESET and CSB) enable
greater flexibility for system design-in of the AD9957.
With the AD9957, the Instruction Byte specifies read/write opera-
tion and register address. Serial operations on the AD9957 occur
only at the register level, not the byte level due to the lack of byte
address space in the Instruction Byte.
For the AD9957, the serial port controller recognizes the register
address in the Instruction Byte and expects that all bytes of that
register will be accessed, otherwise, the serial port controller will be
out of sequence for the next write routine. However, one way to
write less bytes than required is to use the IORESET feature. The
IORESET function can be used to abort an IO operation and reset
the pointer in the serial port controller. After an IORESET, the next
byte will be the instruction byte. Every byte that is written prior to
the IORESET is preserved. Partial bytes are not preserved.
GENERAL OPERATION OF THE SERIAL INTERFACE
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SCLK
SDIO
SCLK
SDO
SDIO
CS
CS
I
I
7
7
I
I
6
6
I
INSTRUCTION CYCLE
5
I
INSTRUCTION CYCLE
5
I
I
4
Serial Port Writing Timing—Clock Stall Low
4
I
I
3
3
I
I
2
2
Rev. PrF | Page 21 of 38
I
I
1
1
I
I
0
0
D
D
O7
7
There are two phases to a communication cycle with the AD9957.
Phase 1 is the instruction cycle, which is the writing of an instruc-
tion byte into the AD9957, coincident with the first eight SCLK
rising edges. The instruction byte provides the AD9957 serial port
controller with information regarding the data transfer cycle, which
is Phase 2 of the communication cycle. The Phase 1 instruction
byte defines whether the upcoming data transfer is read or write
and the serial address of the register being accessed
The first eight SCLK rising edges of each communication cycle are
used to write the instruction byte into the AD9957. The remaining
SCLK edges are for Phase 2 of the communication cycle. Phase 2 is
the actual data transfer between the AD9957 and the system con-
troller. The number of bytes transferred during Phase 2 of the
communication cycle is a function of the register being accessed.
For example, when accessing the Control Function Register #2,
which is four bytes wide, Phase 2 requires that four bytes be trans-
ferred. If accessing the Amplitude Scale Factor Register, which is
two bytes wide, Phase 2 requires that two bytes be transferred. After
transferring all data bytes per the instruction, the communication
cycle is completed.
At the completion of any communication cycle, the AD9957 serial
port controller expects the next 8 rising SCLK edges to be the in-
struction byte of the next communication cycle.
All data input to the AD9957 is registered on the rising edge of
SCLK. All data is driven out of the AD9957 on the falling edge of
SCLK.
The Figures below are useful in understanding the general opera-
tion of the AD9957 Serial Port.
D
D
6
O6
DATA TRANSFER CYCLE
D
D
DATA TRANSFER CYCLE
5
O5
D
D
DON'T CARE
4
O4
D
D
3
O3
D
D
2
O2
D
D
1
O1
D
0
D
O0
AD9957