SERIAL CONTROL PORT
The AD9520 serial control port is a flexible, synchronous serial
communications port that allows an easy interface with many
industry-standard microcontrollers and microprocessors. The
AD9520 serial control port is compatible with most synchronous
transfer formats, including Philips I2C, Motorola® SPI®, and
Intel® SSR® protocols. The AD9520 I2C implementation deviates
from the classic I2C specification on two specifications, and these
deviations are documented in Table 14. The serial control port
allows read/write access to all registers that configure the AD9520.
SPI/I²C PORT SELECTION
The AD9520 has two serial interfaces, SPI and I2C. Users can
select either SPI or I2C depending on the states of the three
logic level (high, open, low) input pins, SP1 and SP0. When
both SP1 and SP0 are high, SPI interface is active. Otherwise,
I2C is active with eight different I2C slave address (seven bits
wide) settings, see Table 40. The four MSBs of the slave address
are hardware coded as 1011 and the three LSBs are
programmed by SP1 and SP0.
Table 40. Serial Port Mode Selection
I²C SERIAL PORT OPERATION
The AD9520 I2C port is designed based on the I2C fast mode
standard. The AD9520 supports both I2C protocols: standard
mode (100 kHz) and fast mode (400 kHz).
The AD9520 I2C port has a 2-wire interface consisting of a serial
data line (SDA) and a serial clock line (SCL). In an I2C bus system,
the AD9520 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 AD9520. The AD9520 uses direct 16-bit (2 bytes) memory
addressing instead of traditional 8-bit (1 byte) memory addressing.
I2C Bus Characteristics
Table 41. I2C Bus Definitions
One pulse on the SCL clock line is generated for each data bit
The data on the SDA line must not change during the high
period of the clock. The state of the data line can only change when
the clock on the SCL line is low.
Figure 53. 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 initial 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 data transfer.
Figure 54. Start and Stop Condition
A byte on the SDA line is always 8-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 done by pulling the SDA line low during the
ninth clock pulse after each 8-bit data byte.
Rev. 0 | Page 51 of 84