Datasheet

AD9523 Data Sheet
Rev. C | Page 32 of 60
valid). Streaming mode does not skip over reserved or blank
registers.
The default mode of the AD9523 serial control port is the
bidirectional mode. In bidirectional mode, both the sent data
and the readback data appear on the SDIO pin. It is also possible to
set the AD9523 to unidirectional mode. In unidirectional mode,
the readback data appears on the SDO pin.
A readback request reads the data that is in the serial control port
buffer area or the data that is in the active registers (see Figure 37).
SERIAL
CONTROL
PORT
BUFFER
REGISTERS
UPDATE
REGISTERS
ACTIVE
REGISTERS
SCLK/SCL
SDO
SDIO/SDA
CS
08439-035
Figure 37. Relationship Between Serial Control Port Buffer Registers and
Active Registers
SPI INSTRUCTION WORD (16 BITS)
The MSB of the instruction word is R/
W
, which indicates
whether the instruction is a read or a write. The next two bits
([W1:W0]) indicate the length of the transfer in bytes. The final
13 bits are the address ([A12:A0]) at which to begin the read or
write operation.
For a write, the instruction word is followed by the number of
bytes of data indicated by Bits[W1:W0] (see Table 25).
Table 25. Byte Transfer Count
W1 W0 Bytes to Transfer
0 0 1
0 1 2
1 0 3
1
1
Streaming mode
Bits[A12:A0] select the address within the register map that is
written to or read from during the data transfer portion of the
communications cycle. Only Bits[A11:A0] are needed to cover
the range of the 0x234 registers used by the AD9523. Bit A12 must
always be 0. For multibyte transfers, this address is the starting
byte address. In MSB first mode, subsequent bytes decrement the
address.
SPI MSB/LSB FIRST TRANSFERS
The AD9523 instruction word and byte data can be MSB first
or LSB first. Any data written to Register 0x000 must be mirrored:
Bit 7 is mirrored to Bit 0, Bit 6 to Bit 1, Bit 5 to Bit 2, and Bit 4 to
Bit 3. This makes it irrelevant whether LSB first or MSB first is
in effect. The default for the AD9523 is MSB first.
When LSB first is set by Register 0x000, Bit 1 and Register 0x000,
Bit 6, it takes effect immediately because it affects only the
operation of the serial control port and does not require that an
update be executed.
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 data byte. Subsequent
data bytes must follow in order from the high address to the
low address. In MSB first mode, the serial control port internal
address generator decrements for each data byte of the multibyte
transfer cycle.
When LSB first mode is active, 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 data byte, followed by
multiple data bytes. In a multibyte transfer cycle, the internal
byte address generator of the serial port increments for each byte.
The AD9523 serial control port register address decrements
from the register address just written toward 0x000 for multibyte
I/O operations if the MSB first mode is active (default). If the
LSB first mode is active, the register address of the serial control
port increments from the address just written toward 0x234 for
multibyte I/O operations. Unused addresses are not skipped for
these operations.
For multibyte accesses that cross Address 0x234 or Address 0x000
in MSB first mode, the SPI internally disables writes to subsequent
registers and returns zeros for reads to subsequent registers.
Streaming mode always terminates when crossing address
boundaries (as shown in Table 26).
Table 26. Streaming Mode (No Addresses Are Skipped)
Write Mode Address Direction Stop Sequence
MSB First Decrement …, 0x001, 0x000, stop
Table 27. Serial Control Port, 16-Bit Instruction Word, MSB First
MSB LSB
I15 I14 I13 I12 I11 I10 I9 I8 I7 I6 I5 I4 I3 I2 I1 I0
R/
W
W1 W0 A12 = 0 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0