1.3 TEMPERATURE DATA FORMAT

Temperature data is represented by a 14-bit, two’s comple-

ment word with an LSB (Least Significant Bit) equal to

0.03125˚C:

Temperature

Digital Output

Binary

Hex

+150˚C

0100 1011 0000 0011

4B03

+125˚C

0011 1110 1000 0011

3E83

+25˚C

0000 1100 1000 0011

0C83

+0.03125˚C

0000 0000 0000 0111

0007

0˚C

0000 0000 0000 0011

0003

−0.03125˚C

1111 1111 1111 1111

FFFF

−25˚C

1111 0011 1000 0011

F383

−40˚C

1110 1100 0000 0011

EC03

The first data byte is the most significant byte with most

significant bit first, permitting only as much data as neces-

sary to be read to determine temperature condition. For

instance, if the first four bits of the temperature data indicate

an overtemperature condition, the host processor could im-

mediately take action to remedy the excessive tempera-

tures.

1.4 SHUTDOWN MODE/MANUFACTURER’S ID

Shutdown mode is enabled by writing XX FF to the LM71 as

shown in Figure 7c. The serial bus is still active when the

LM71 is in shutdown. When in shutdown mode the LM71

always will output 1000 0000 0000 1111. This is the

manufacturer’s/Device ID information. The first 5-bits of the

field (1000 0XXX) are reserved for manufacturer’s ID.

1.5 INTERNAL REGISTER STRUCTURE

The LM71 has three registers, the temperature register, the

configuration register and the manufacturer’s/device identifi-

cation register. The temperature and manufacturer’s/device

identification registers are read only. The configuration reg-

ister is write only.

1.5.1 Configuration Register

(Selects shutdown or continuous conversion modes):

(Write Only):

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

X

XXXXXXX

Shutdown

D0–D15 set to XX FF hex enables shutdown mode.

D0–D15 set to 00 00 hex sets Continuous conversion mode.

Note: setting D0-D15 to any other values may place the LM70 into a manufacturer’s test mode, upon which the LM71 will stop

responding as described. These test modes are to be used for National Semiconductor production testing only. See Section 1.2

Serial Bus Interface for a complete discussion.

1.5.2 Temperature Register

(Read Only):

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

MSB

Bit 12

Bit 11

Bit 10

Bit 9

Bit 8

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit1

LSB

1

1

D0–D1: Logic 1 will be output on SI/0.

D2–D15: Temperature Data. One LSB = 0.03125˚C. Two’s complement format.

1.5.3 Manufacturer/Device ID Register

(Read Only):

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

1

00000000000111

1

D0–D1: Logic 1 will be output on SI/0.

D2–D15: Manufacturer’s/Device ID Data. This register is accessed whenever the LM71 is in shutdown mode.

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