DS3904/DS3905
Triple 128-Position Nonvolatile Digital
Variable Resistor/Switch
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implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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11
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is a registered trademark of Dallas Semiconductor Corporation.
The DS3904/DS3905 can operate in the following three
modes:
1) Slave Receiver Mode: Serial data and clock are
received through SDA and SCL, respectively. After
each byte is received, an acknowledge bit is trans-
mitted. Start and stop conditions are recognized as
the beginning and end of a serial transfer. Address
recognition is performed by hardware after the
slave (device) address and direction bit has been
received.
2) Slave Transmitter Mode: The first byte is received
and handled as in the slave receiver mode.
However, in this mode the direction bit indicates
that the transfer direction is reversed. Serial data is
transmitted on SDA by the DS3904/DS3905 while
the serial clock is input on SCL. Start and stop con-
ditions are recognized as the beginning and end of
a serial transfer.
3) Slave Address: The command/control byte is the
first byte received following the start condition from
the master device. The command/control byte con-
sists of a 4-bit device identifier. For the DS3904, the
identifier is followed by the device-select bits 0, 0,
and A0. For the DS3905, the identifier is followed by
the device-select bits A2, A1, A0. The device identi-
fier is used by the master device to select which
device is to be accessed. When reading or writing
the DS3904/DS3905, the device-select bits must
match the device-select pin(s). The last bit of the
command/control byte (R/W) defines the operation
to be performed. When set to a ‘1’, a read operation
is selected, and when set to a ‘0’, a write operation
is selected.
Following the start condition, the DS3904/DS3905 moni-
tor the SDA bus checking the device-type identifier
being transmitted. Upon receiving the control code, the
appropriate device address bit, and the read/write bit,
the slave device outputs an acknowledge signal on the
SDA line.
Applications Information
Power-Supply Decoupling
To achieve the best results when using the DS3904/
DS3905, decouple the power supply with a 0.01µF or
0.1µF capacitor. Use a high-quality ceramic surface-
mount capacitor. Surface-mount components minimize
lead inductance, which improves performance, and
ceramic capacitors tend to have adequate high-fre-
quency response for decoupling applications.
High Resistor Terminal Voltage
It is possible to have a voltage on the resistor-high termi-
nals that is higher than the voltage connected to V
CC
.
For instance, connecting V
CC
to 3.0V while one or more
of the resistor high terminals are connected to 5.0V
allows a 3V system to control a 5V system. The 5.5V
maximum still applies to the limit on the resistor high ter-
minals regardless of the voltage present on V
CC
.
Package Information
For the latest package outline information, go to
www.maxim-ic.com/DallasPackInfo.
