AD5382
I2C SERIAL INTERFACE
AD5382 Slave Addresses
The AD5382 features an I2C compatible 2-wire interface
consisting of a serial data line (SDA) and a serial clock line
(SCL). SDA and SCL facilitate communication between the
AD5382 and the master at rates up to 400 kHz. Figure 6 shows
the 2-wire interface timing diagrams that incorporate three
different modes of operation. In selecting the I2C operating
A bus master initiates communication with a slave device by
issuing a START condition followed by the 7-bit slave address.
When idle, the AD5382 waits for a START condition followed
by its slave address. The LSB of the address word is the Read/
Write (R/ ) bit. The AD5382 is a receive only device; when
W
mode, first configure serial operating mode (SER/
= 1) and
PAR
communicating with the AD5382, R/ = 0. After receiving the
W
proper address 1010 1AD1AD0 , the AD5382 issues an ACK by
pulling SDA low for one clock cycle.
then select I2C mode by configuring the
/I2C pin to a
SPI
Logic 1. The device is connected to the I2C bus as a slave device
(i.e., no clock is generated by the AD5382). The AD5382 has a
7-bit slave address 1010 1AD1AD0. The 5 MSB are hard-coded
and the 2 LSB are determined by the state of the AD1 and AD0
pins. The facility to hardware configure AD1 and AD0 allows
four of these devices to be configured on the bus.
The AD5382 has four different user programmable addresses
determined by the AD1 and AD0 bits.
Write Operation
There are three specific modes in which data can be written to
the AD5382 DAC.
I2C Data Transfer
One data bit is transferred during each SCL clock cycle. The
data on SDA must remain stable during the high period of the
SCL clock pulse. Changes in SDA while SCL is high are control
signals that configure START and STOP conditions. Both SDA
and SCL are pulled high by the external pull-up resistors when
the I2C bus is not busy.
4-Byte Mode
When writing to the AD5382 DACs, the user must begin with
an address byte (R/ = 0) after which the DAC will acknowl-
W
edge that it is prepared to receive data by pulling SDA low. The
address byte is followed by the pointer byte; this addresses the
specific channel in the DAC to be addressed and is also
acknowledged by the DAC. Two bytes of data are then written
to the DAC, as shown in Figure 31. A STOP condition follows.
This allows the user to update a single channel within the
AD5382 at any time and requires four bytes of data to be
transferred from the master.
START and STOP Conditions
A master device initiates communication by issuing a START
condition. A START condition is a high-to-low transition on
SDA with SCL high. A STOP condition is a low-to-high
transition on SDA while SCL is high. A START condition from
the master signals the beginning of a transmission to the
AD5382. The STOP condition frees the bus. If a repeated
START condition (Sr) is generated instead of a STOP condition,
the bus remains active.
3-Byte Mode
In 3-byte mode, the user can update more than one channel in a
write sequence without having to write the device address byte
each time. The device address byte is only required once; sub-
sequent channel updates require the pointer byte and the data
bytes. In 3-byte mode, the user begins with an address byte
Repeated START Conditions
A repeated START (Sr) condition may indicate a change of data
direction on the bus. Sr may be used when the bus master is
writing to several I2C devices and wants to maintain control of
the bus.
(R/ = 0), after which the DAC will acknowledge that it is
W
prepared to receive data by pulling SDA low. The address byte is
followed by the pointer byte. This addresses the specific channel
in the DAC to be addressed and is also acknowledged by the
DAC. This is then followed by the two data bytes. REG1 and
REG0 determine the register to be updated.
Acknowledge Bit (ACK)
The acknowledge bit (ACK) is the ninth bit attached to any
8-bit data-word. ACK is always generated by the receiving
device. The AD5382 devices generate an ACK when receiving
an address or data by pulling SDA low during the ninth clock
period. Monitoring ACK allows for detection of unsuccessful
data transfers. An unsuccessful data transfer occurs if a
receiving device is busy or if a system fault has occurred. In the
event of an unsuccessful data transfer, the bus master should
reattempt communication.
If a STOP condition does not follow the data bytes, another
channel can be updated by sending a new pointer byte followed
by the data bytes. This mode only requires three bytes to be sent
to update any channel once the device has been initially
addressed, and reduces the software overhead in updating the
AD5382 channels. A STOP condition at any time exits this
mode. Figure 32 shows a typical configuration.
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