AD9508 Datasheet, PDF (27/40 Pages) Analog Devices – 1.65 GHz Clock Fanout Buffer with Output Dividers and Delay Adjust

Data Sheet
AD9508
Write
When the instruction word indicates a write operation, the payload
is written into the serial control port buffer of the AD9508. Data
bits are registered on the rising edge of SCLK. The length of the
transfer (one, two, or three bytes or streaming mode) depends
on the W0 and W1 bits in the instruction byte. When not
streaming,
CS^E
A
A
can
be
deasserted
after
each
sequence
of
eight
bits to stall the bus (except after the last byte, where it ends the
c
ycle).
When
the
bus
is
stalled,
the
serial
transfer
resumes
when
CS^E
A
A
is
asserted.
Deasserting
the
CS^E
A
A
pin
on
a
nonbyte
boundary
resets
the serial control port. Reserved or blank registers are not skipped
automatically during a write sequence. Therefore, the user must
know what bit pattern to write to the reserved registers to preserve
proper operation of the device. Generally, it does not matter what
data is written to blank registers, but it is customary to write 0s.
Most of the serial port registers are buffered. This means that
data written into buffered registers do not take effect until the
user issues an I/O update. An I/O update operation is executed
by writing a Logic 1 to Register 0x0005, Bit 0 (which is an auto-
clearing bit) or by programming a multifunction pin to perform
the I/O update function and applying an external signal to that
pin. The user can change as many register bits as needed before
executing an I/O update. The I/O update operation transfers the
buffer register contents to their active register counterparts.
Read
The AD9508 supports the long instruction mode only. If the
instruction word indicates a read operation, the next N × 8
SCLK cycles clock out the data from the address specified in
the instruction word. N is the number of data bytes read and
depends on the W0 and W1 bits of the instruction word. The
readback data is valid on the falling edge of SCLK. Blank registers
are not skipped during readback.
A readback operation takes data from either the serial control
port buffer registers or the active registers.
SPI Instruction Word (16 Bits)
The
MSB
of
the
16-bit
instruction
word
is
R/W,^E
A
A
which
indicates
whether the instruction is a read or a write. The next two bits, W1
and W0, indicate the number of bytes in the transfer. The final 13
bits are the register address (A12 to A0), which indicates the
starting register address of the read/write operation (see Table 19).
SPI MSB First and LSB First Transfers
The AD9508 instruction word and payload can be MSB first or
LSB first; the default is MSB first. The LSB first mode can be set by
writing a 1 to Register 0x00, Bit 6. Immediately after the LSB first
bit is set, subsequent serial control port operations are LSB first.
When MSB first mode is active, the instruction and data bytes
must be written from MSB to LSB. Multibyte data transfers in
MSB first format start with an instruction byte that includes the
register address of the most significant payload byte. Subsequent
data bytes must follow, in order, from high address to low address.
In MSB first mode, the serial control port internal address genera-
tor decrements for each data byte of the multibyte transfer cycle.
When Register 0x00, Bit 6 = 1 (LSB first), the instruction and
data bytes must be written from LSB to MSB. Multibyte data
transfers in LSB first format start with an instruction byte that
includes the register address of the least significant payload byte,
followed by multiple data bytes. The serial control port internal
byte address generator increments for each byte of the multibyte
transfer cycle.
For multibyte MSB first (default) I/O operations, the serial control
port register address decrements from the specified starting address
toward Address 0x00. For multibyte LSB first I/O operations, the
serial control port register address increments from the starting
address toward Address 0x2C. Reserved addresses are not skipped
during multibyte I/O operations; therefore, the user writes the
default value to a reserved register and writes 0s to unmapped
registers. Note that it is more efficient to issue a new write
command than to write the default value to more than two
consecutive reserved (or unmapped) registers.
Table 18. Streaming Mode (No Addresses Skipped)
Write Mode Address Direction Stop Sequence
LSB First
Increment
0x00 … 0x2C
MSB First
Decrement
0x2C … 0x00
Table 19. Serial Control Port, 16-Bit Instruction Word, MSB First Bit Map
MSB
LSB
I15
I14 I13 I12
I11
I10
I9
I8 I7
I6
I5 I4 I3
I2
I1 I0
R/W^E
W1 W0 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
A
CS
SCLK DON'T CARE
DON'T CARE
SDIO DON'T CARE R/W W1 W0 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
16-BIT INSTRUCTION HEADER
REGISTER (N) DATA
REGISTER (N – 1) DATA
DON'T CARE
Figure 48. Serial Control Port Write—MSB First, 16-Bit Instruction, Two Bytes of Data
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