1.5 INTERNAL REGISTER STRUCTURE

The LM74A 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

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 LM74A 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 11

Bit 10

Bit 9

Bit 8

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

LSB

1

X

X

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

D2: Always set high.

D3–D15: Temperature Data. One LSB = 0.0625˚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

1

0000000000000

X

X

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

D2–D15: Manufacturer’s/Device ID Data. This register is accessed whenever the LM74A is in shutdown mode.

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