Datasheet

DS3903
Triple 128-Position Nonvolatile
Digital Potentiometer
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write process t
w
to the EEPROM memory. All inputs are
disabled during this write cycle.
The DS3903 is capable of an 8-byte page write. A page
write is initiated the same way as a byte write, but the
master does not send a stop condition after the first
data byte. Instead, after the slave acknowledges the
data byte has been received, the master can send up
to seven more data bytes using the same nine-clock
sequence. After a write to the last byte in the page, the
address returns to the beginning of the same page.
The master must then terminate the write cycle with a
stop condition or the data clocked into the DS3903 is
not latched into EEPROM. Note that in order for eight
bytes to be stored sequentially (and to prevent looping
around), the address byte must be set to the beginning
of the desired page (three LSBs of the address are 0).
For detailed information concerning page operations,
see the Potentiometer Memory Organization section.
Acknowledge Polling
Once the internally timed write has started and the
DS3903 inputs are disabled, acknowledge polling can
be initiated. The process involves transmitting a start
condition followed by the device address. The R/W bit
signifies the type of operation that is desired. The read
or write sequence is only allowed to proceed if the
internal write cycle has completed and the DS3903
responds with a zero.
Read Operations
After receiving a matching address byte with the R/W bit
set high, the device goes into the read mode of opera-
tion. There are three read operations: current address
read, random read, and sequential address read.
Current Address Read
The DS3903 has an internal address register that main-
tains the address used during the last read or write
operation, incremented by one. This data is maintained
as long as V
CC
is valid. If the most recent address was
the last byte in memory, then the register resets to the
first address. This address stays valid between opera-
tions as long as power is available.
Once the device address is clocked in and acknowl-
edged by the DS3903 with the R/W bit set to high, the
current address data word is clocked out. The master
does not respond with a zero, but does generate a stop
condition afterwards.
Random Address Read
A random read requires a dummy byte write sequence
to load in the data word address. Once the device
address and data address bytes are clocked in by the
master, and acknowledged by the DS3903, the master
must generate another start condition. The master now
initiates a current address read by sending the device
address with the R/W bit set high. The DS3903
acknowledges the device address and serially clocks
out the data byte.
Sequential Address Read
Sequential reads are initiated by either a current
address read or a random address read. After the mas-
ter receives the first data byte, the master responds
with an acknowledge. As long as the DS3903 receives
this acknowledge after a byte is read, the master can
clock out additional data words from the DS3903. After
reaching address FFh, it resets to address 00h.
The sequential read operation is terminated when the
master initiates a stop condition. The master does not
respond with a zero.
For a more detailed description of 2-wire theory of
operation, see the following section.
2-Wire Serial Port Operation
The 2-wire serial port interface supports a bidirectional
data transmission protocol with device addressing. A
device that sends data on the bus is defined as a trans-
mitter, and a device receiving data as a receiver. The
device that controls the message is called a “master.”
The devices that are controlled by the master are
“slaves.” The bus must be controlled by a master
device that generates the serial clock (SCL), controls
the bus access, and generates the start and stop con-
ditions. The DS3903 operates as a slave on the 2-wire
bus. Connections to the bus are made through the
open-drain I/O lines, SDA and SCL. The following I/O
terminals control the 2-wire serial port: SDA, SCL, and
A0. Timing diagrams for the 2-wire serial port can be
found in Figures 2 and 3. Timing information for the 2-
wire serial port is provided in the AC Electrical
Characteristics table for 2-wire serial communications.