DS75LVSTR 查看數據表（PDF） - Maxim Integrated

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DS75LVSTR

Digital Thermometer and Thermostat

Maxim Integrated 

DS75LV

Digital Thermometer and Thermostat

Register Pointer

The four DS75LV registers each have a unique 2-bit

pointer designation, which is defined in Table 5. When

reading from or writing to the DS75LV, the user must

“point” the DS75LV to the register that is to be accessed.

When reading from the DS75LV, once the pointer is set,

it remains pointed at the same register until it is changed.

For example, if the user desires to perform consecutive

reads from the temperature register, then the pointer only

has to be set to the temperature register one time, after

which all reads are automatically from the temperature

register until the pointer value is changed. When writing

to the DS75LV, the pointer value must be refreshed each

time a write is performed, even if the same register is

being written to twice in a row.

At power-up, the pointer defaults to the temperature

register location. The temperature register can be read

immediately without resetting the pointer.

Changes to the pointer setting are accomplished as

described in the 2-Wire Serial Data Bus section of this

data sheet.

2-Wire Serial Data Bus

The DS75LV communicates over a standard bidirectional

2-wire serial data bus that consists of a serial clock (SCL)

signal and serial data (SDA) signal. The device interfaces

to the bus via the SCL input pin and open-drain SDA I/O

pin. All communication is MSb first.

The following terminology is used to describe 2-wire

communication:

Master Device: Microprocessor/microcontroller that controls

the slave devices on the bus. The master device generates

the SCL signal and START and STOP conditions.

Slave: All devices on the bus other than the master. The

DS75LV always functions as a slave.

Bus Idle or Not Busy: Both SDA and SCL remain high.

SDA is held high by a pullup resistor when the bus is idle,

and SCL must either be forced high by the master (if the

SCL output is push-pull) or pulled high by a pullup resistor

(if the SCL output is open-drain).

Transmitter: A device (master or slave) that is sending

data on the bus.

Receiver: A device (master or slave) that is receiving data

from the bus.

START Condition: Signal generated by the master to

indicate the beginning of a data transfer on the bus. The

master generates a START condition by pulling SDA from

high to low while SCL is high (see Figure 6). A “repeated”

START is sometimes used at the end of a data transfer

(instead of a STOP) to indicate that the master will

perform another operation.

STOP Condition: Signal generated by the master to

indicate the end of a data transfer on the bus. The master

generates a STOP condition by transitioning SDA from

low to high while SCL is high (see Figure 6). After the

STOP is issued, the master releases the bus to its idle state.

Acknowledge (ACK): When a device (either master

or slave) is acting as a receiver, it must generate an

acknowledge (ACK) on the SDA line after receiving every

byte of data. The receiving device performs an ACK by

pulling the SDA line low for an entire SCL period (see

Figure 6). During the ACK clock cycle, the transmitting

device must release SDA. A variation on the ACK signal is

the “not acknowledge” (NACK). When the master device

is acting as a receiver, it uses a NACK instead of an ACK

after the last data byte to indicate that it is finished receiv-

ing data. The master indicates a NACK by leaving the

SDA line high during the ACK clock cycle.

Slave Address: Every slave device on the bus has a

unique 7-bit address that allows the master to access that

device. The DS75LV’s 7-bit bus address is 1 0 0 1 A2 A1

A0, where A2, A1, and A0 are user-selectable via the cor-

responding input pins. The three address pins allow up

to eight DS75LVs to be multi-dropped on the same bus.

Address Byte: The control byte is transmitted by the

master and consists of the 7-bit slave address plus a

read/write (R/W) bit (see Figure 7). If the master is going

to read data from the slave device then R/W = 1, and if

the master is going to write data to the slave device then

R/W = 0.

Pointer Byte: The pointer byte is used by the master to

tell the DS75LV which register is going to be accessed

during communication. The six MSbs of the pointer byte

(see Figure 8) are always 0 and the two LSbs correspond

to the desired register as shown in Table 5.

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