1.3 TEMPERATURE DATA FORMAT

Temperature data is represented by a 11-bit, two’s comple-

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

0.25˚C:

Temperature

Digital Output

Binary

Hex

+150˚C

0100 1011 0001 1111

4B 1Fh

+125˚C

0011 1110 1001 1111

3E 9Fh

+25˚C

0000 1100 1001 1111

0B 9Fh

+0.25˚C

0000 0000 0011 1111

00 3Fh

0˚C

0000 0000 0001 1111

00 1Fh

−0.25˚C

1111 1111 1111 1111

FF FFh

−25˚C

1111 0011 1001 1111

F3 9Fh

−55˚C

1110 0100 1001 1111

E4 9Fh

Note: The last two bits are TRI-STATE and depicted as one

in the table.

The first data byte is the most significant byte with most sig-

nificant bit first, permitting only as much data as necessary to

be read to determine temperature condition. For instance, if

the first four bits of the temperature data indicate an over-

temperature condition, the host processor could immediately

take action to remedy the excessive temperatures.

1.4 SHUTDOWN MODE/MANUFACTURER’S ID

Shutdown mode is enabled by writing XX FF to the LM70 as

shown in

Figure 7c and discussed in Section 1.2. The serial

bus is still active when the LM70 is in shutdown. Current

draw drops to less than 10 µA between serial communica-

tions. When in shutdown mode the LM70 always will output

1000 0001 0000 00XX. This is the manufacturer’s ID/Device

ID information. The first 5-bits of the field (1000 0XXX) are

reserved for manufacturer’s ID.

1.5 INTERNAL REGISTER STRUCTURE

The LM70 has three registers, the temperature register, the configuration register and the manufacturer’s/device identification

register. The temperature and manufacturer’s/device identification registers are read only. The configuration register 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

XXXXXXXX

Shutdown

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

D0-D15 set to XX 00 hex enables continuous conversion mode.

Note: setting D0-D15 to any other values may place the LM70 into a manufacturer’s test mode, upon which the LM70 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 9

Bit 8

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

LSB

1

1

1

X

X

D0–D1: Undefined. TRI-STATE will be output on SI/0.

D2–D4: Always set high.

D5–D15: Temperature Data. One LSB = 0.25˚C. Two’s complement format.

1.5.3 MANUFACTURER’S/DEVICE ID REGISTER

(Read Only):

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

10000001000000

X

X

D0–D1: Undefined. TRI-STATE will be output on SI/0.

D2-D4: Always set LOW.

D5–D15: Manufacturer’s ID Data. This register is accessed whenever the LM70 is in shutdown mode.

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