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DS1848E-010+

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
DS1848
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2-WIRE SERIAL PORT OPERATION
The 2-wire serial port interface supports a bi-directional data transmission protocol with device
addressing. A device that sends data on the bus is defined as a transmitter, 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 conditions. The DS1848 operates as
a slave on the 2-wire bus. Connections to the bus are made via the open-drain I/O lines SDA and SCL.
The following I/O terminals control the 2-wire serial port: SDA, SCL, A0, A1, A2. Timing diagrams for
the 2-wire serial port can be found in Figures 3 and 4. Timing information for the 2-wire serial port is
provided in the AC Electrical Characteristics Table for 2-wire serial communications.
The following bus protocol has been defined:
§ Data transfer may be initiated only when the bus is not busy.
§ During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in
the data line while the clock line is HIGH will be interpreted as control signals.
Accordingly, the following bus conditions have been defined:
Bus not busy: Both data and clock lines remain HIGH.
Start data transfer: A change in the state of the data line from HIGH to LOW while the clock is HIGH
defines a START condition.
Stop data transfer: A change in the state of the data line from LOW to HIGH while the clock line is
HIGH defines the STOP condition.
Data valid: The state of the data line represents valid data when, after a START condition, the data line
is stable for the duration of the HIGH period of the clock signal. The data on the line can be changed
during the LOW period of the clock signal. There is one clock pulse per bit of data. Figures 3 and 4 detail
how data transfer is accomplished on the two-wire bus. Depending upon the state of the R/W bit, two
types of data transfer are possible.
Each data transfer is initiated with a START condition and terminated with a STOP condition. The
number of data bytes transferred between START and STOP conditions is not limited and is determined
by the master device. The information is transferred byte-wise and each receiver acknowledges with a
ninth bit.
Within the bus specifications a regular mode (100kHz clock rate) and a fast mode (400kHz clock rate) are
defined. The DS1848 works in both modes.
Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge after the
reception of each byte. The master device must generate an extra clock pulse that is associated with this
acknowledge bit.
A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a
way that the SDA line is a stable LOW during the HIGH period of the acknowledge-related clock pulse.
Of course, setup and hold times must be taken into account. A master must signal an end of data to the
DS1848
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slave by not generating an acknowledge bit on the last byte that has been clocked out of the slave. In this
case, the slave must leave the data line HIGH to enable the master to generate the STOP condition.
1. Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the master is
the command/control byte. Next follows a number of data bytes. The slave returns an acknowledge bit
after each received byte.
2. Data transfer from a slave transmitter to a master receiver. The master transmits the first byte (the
command/control byte) to the slave. The slave then returns an acknowledge bit. Next follows a
number of data bytes transmitted by the slave to the master. The master returns an acknowledge bit
after all received bytes other than the last byte. At the end of the last received byte, a ‘not
acknowledge’ can be returned.
The master device generates all serial clock pulses and the START and STOP conditions. A transfer is
ended with a STOP condition or with a repeated START condition. Since a repeated START condition is
also the beginning of the next serial transfer, the bus will not be released.
The DS1848 may operate in the following two 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 transmitted. START and STOP conditions are recognized
as the beginning and end of a serial transfer. Address recognition is performed by hardware after
reception of the slave (device) address and direction bit.
2. Slave transmitter mode: The first byte is received and handled as in the slave receiver mode.
However, in this mode the direction bit will indicate that the transfer direction is reversed. Serial data
is transmitted on SDA by the DS1848, while the serial clock is input on SCL. START and STOP
conditions are recognized as the beginning and end of a serial transfer.
3. Slave Address: Command/control byte is the first byte received following the START condition from
the master device. The command/control byte consists of a 4-bit control code. For the DS1848, this is
set as 1010 binary for read/write operations. The next 3 bits of the command/ control byte are the
device select bits or slave address (A2, A1, A0). They are used by the master device to select which
of eight devices is to be accessed. When reading or writing the DS1848, the device-select bits must
match the device-select pins (A2, A1, A0). 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 DS1848 monitors the SDA bus checking the device type identifier
being transmitted. Upon receiving the 1010 control code, the appropriate device address bits, and the
read/write bit, the slave device outputs an acknowledge signal on the SDA line.
WRITE PROTECT
The write-protect input pin (WP) protects all memory (including EEPROM), control registers, and look-
up tables from alteration in an application. However, this does not interfere with internal
temperature/resistor updates. If set to a logic 0, the device is not write protected and can be written to via
the 2-wire interface. This pin has an internal pull-up resistor.
DS1848
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2-WIRE DATA TRANSFER PROTOCOL Figure 3
2-WIRE AC CHARACTERISTICS Figure 4
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

DS1848E-010+

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Buy DS1848E-010+
Manufacturer:
Maxim Integrated
Description:
Digital Potentiometer ICs Dual Temp Controlled NV Variable Resistor
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