EVAL-ADN2804EBZ datasheet(18/24 Pages) AD

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ADN2804

Data Sheet

Rev. D | Page 18 of 24

To control the device on the bus, the following protocol must be

followed. First, the master initiates a data transfer by establish-

ing a start condition, defined by a high-to-low transition on

SDA while SCK remains high. This indicates that an address/

data stream follows. All peripherals respond to the start condition

and shift the next eight bits (the 7-bit address and the R/W bit).

The bits are transferred from MSB to LSB. The peripheral that

recognizes the transmitted address responds by pulling the data

line low during the ninth clock pulse. This is known as an

acknowledge bit. All other devices withdraw from the bus at

this point and maintain an idle condition. The idle condition is

where the device monitors the SDA and SCK lines, waiting for

the start condition and correct transmitted address. The R/W

bit determines the direction of the data. Logic 0 on the LSB of

the first byte means that the master writes information to the

peripheral. Logic 1 on the LSB of the first byte means that the

master reads information from the peripheral.

The ADN2804 acts as a standard slave device on the bus. The data

on the SDA pin is eight bits long, supporting the 7-bit addresses

plus the R/W bit. The ADN2804 has eight subaddresses to enable

the user-accessible internal registers (see Table 6 through

Table 10). It, therefore, interprets the first byte as the device

address and the second byte as the starting subaddress. Auto-

increment mode is supported, allowing data to be read from or

written to the starting subaddress and each subsequent address

without manually addressing the subsequent subaddress. A data

transfer is always terminated by a stop condition. The user can

also access any unique subaddress register on a one-by-one

basis without updating all registers.

Stop and start conditions can be detected at any stage of the

data transfer. If these conditions are asserted out of sequence

with normal read and write operations, they cause an immediate

jump to the idle condition. During a given SCK high period, the

user should issue one start condition, one stop condition, or a

single stop condition followed by a single start condition. If an

invalid subaddress is issued by the user, the ADN2804 does not

issue an acknowledge and returns to the idle condition. If the

user exceeds the highest subaddress while reading back in auto-

increment mode, then the highest subaddress register contents

continue to be output until the master device issues a no acknow-

ledge. This indicates the end of a read. In a no-acknowledge

condition, the SDATA line is not pulled low on the ninth pulse.

See Figure 8 and Figure 9 for sample write and read data transfers

and Figure 10 for a more detailed timing diagram.

Additional Features Available via the I2C Interface

LOS Configuration

The LOS detector output, Pin 22, can be configured to be either

active high or active low. If CTRLC[2] is set to Logic 0 (default),

the LOS pin is active high when a loss-of-signal condition is

detected. Writing a 1 to CTRLC[2] configures the LOS pin to be

active low when a loss-of-signal condition is detected.

System Reset

A frequency acquisition can be initiated by writing a 1 followed

by a 0 to the I2C Register Bit CTRLB[5]. This initiates a new

frequency acquisition while keeping the ADN2804 in its

previously programmed operating mode, as set in Registers

CTRL[A], CTRL[B], and CTRL[C].

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