Datasheet

AD9523 Data Sheet
Rev. C | Page 28 of 60
SERIAL CONTROL PORT
The AD9523 serial control port is a flexible, synchronous serial
communications port that allows an easy interface with many
industry-standard microcontrollers and microprocessors. The
AD9523 serial control port is compatible with most synchronous
transfer formats, including Philips IC®, Motorola® SPI, and
Intel® SSR protocols. The AD9523 IC implementation deviates
from the classic IC specification in two specifications, and
these deviations are documented in Table 16 of this data sheet.
The serial control port allows read/write access to all registers
that configure the AD9523.
SPI/I²C PORT SELECTION
The AD9523 has two serial interfaces, SPI and IC. Users can
select either the SPI or IC depending on the states (logic high,
logic low) of the two logic level input pins, SP1 and SP0, when
power is applied or after a
RESET
(each pin has an internal
40 kΩ pull-down resistor).
When both SP1 and SP0 are low,
the SPI interface is active. Otherwise, I
2
C is active with three
different I
2
C slave address settings (seven bits wide), as shown
in
Tabl e 22. The five MSBs of the slave address are hardware
coded as 11000, and the two LSBs are determined by the logic
levels of the SP1 and SP0 pins.
Table 22. Serial Port Mode Selection
SP1 SP0 Address
Low Low SPI
Low High I
2
C: 1100000
High Low I
2
C: 1100001
High High I
2
C: 1100010
I²C SERIAL PORT OPERATION
The AD9523 IC port is based on the IC fast mode standard.
The AD9523 supports both IC protocols: standard mode
(100 kHz) and fast mode (400 kHz).
The AD9523 IC port has a 2-wire interface consisting of a serial
data line (SDA) and a serial clock line (SCL). In an IC bus system,
the AD9523 is connected to the serial bus (data bus SDA and
clock bus SCL) as a slave device, meaning that no clock is generated
by the AD9523. The AD9523 uses direct 16-bit (two bytes)
memory addressing instead of traditional 8-bit (one byte) memory
addressing.
I
2
C Bus Characteristics
Table 23. I
2
C Bus Definitions
Abbreviation Definition
S Start
Sr Repeated start
P Stop
A Acknowledge
A
No acknowledge
W Write
R Read
One pulse on the SCL clock line is generated for each data bit
that is transferred.
The data on the SDA line must not change during the high period
of the clock. The state of the data line can change only when the
clock on the SCL line is low.
SDA
SCL
DATA LINE
STABLE;
DATA VALID
CHANGE
OF DATA
ALLOWED
0
8439-160
Figure 30. Valid Bit Transfer
A start condition is a transition from high to low on the SDA
line while SCL is high. The start condition is always generated
by the master to initialize the data transfer.
A stop condition is a transition from low to high on the SDA
line while SCL is high. The stop condition is always generated
by the master to end the data transfer.
START
CONDITION
S
STOP
CONDITION
P
SD
A
SCL
08439-161
Figure 31. Start and Stop Conditions
A byte on the SDA line is always eight bits long. An acknowledge
bit must follow every byte. Bytes are sent MSB first.
The acknowledge bit is the ninth bit attached to any 8-bit data
byte. An acknowledge bit is always generated by the receiving
device (receiver) to inform the transmitter that the byte has
been received. It is accomplished by pulling the SDA line low
during the ninth clock pulse after each 8-bit data byte.