The minimum scan rate is recommended to be 4Hz (i.e. the measurement data is updated at least once in 250 ms), see Section

2.11 for further details. In Low-Power Mode, the scan rate is four times lower than the scan rate in Active Mode. The scan rate

effects the bus bandwidth required to read the results. The sampling rate of the temperature measurements can also be controlled

via the Conversion Rate register, see Section 2.11 for further details.

Data Readout

When a new result is stored in the Readout register a Function Event is generated. Reading the Readout

register clears the Status Function 1 flag (SF1). The result is available in the Readout register waiting for the master to read it

during the master sensor read sequence. If a new result is ready before the previous result has been read, the new result

overwrites the previous result and the Error Function 1 flag (ERF1) is set (indicating an overrun event). Reading the Readout

register clears also the Error Function 1 flag (ERF1). The Readout register contains the temperature data, and the sensor number.

Since the LM40 only supports three temperature zones the sensor number field will be zero to two. Other fields in the Readout

register as defined by the SensorPath specification are not supported.

Readout Resolution

The resolution of the readout is defined in the Temperature Capabilities register. The resolution of the

LM40 is fixed and cannot be modified by software. The temperature readout type is common to all the sensors and is signed two’s

complement fixed point value. The readout type is specified in the Capabilities register of the function.

Sensor 0 in the Temperature Measurement function is reserved for local temperature measurement (i.e., the junction temperature

of the LM40).

Function Event

The Temperature Measurement function generates a Function Event whenever a conversion cycle is

completed and new data is stored in the Readout Register. When the new data is stored into the Readout register the SF1 bit in

the device Status register is set to "1" and remains set, until it is cleared by reading the Readout register. An Attention Request

is generated on the bus, only if it is enabled by the Attention Enable bit (ATE) in the Temperature Control register.

Setup Before Enabling

No setup is required for the Temperature Measurement function before the function is enabled.

2.9.2 Temperature Capabilities (Addr: 001 000; 08h)

Reg

Add

Register

Name

R/

W

P

O

R

Val

Bit

15

MSb

Bit

14

Bit

13

Bit

12

Bit

11

Bit

10

Bit

9

Bit

8

Bit

7

Bit

6

Bit

5

Bit

4

Bit

3

Bit

2

Bit

1

Bit

0

LSb

001 000

Temperature

Capabilities

R 0549h

Reserved

# of Remotes

Int

Sens

Rout

Size

Sign

10-Bits

0.5˚C

Resolution

0000010101001001

This register defines the format of the temperature data in the readout register. The LM40 only supports one format for all

temperatures as defined by the values of this register.

Bit

Type

Description

2-0

RO

Resolution. This field defines the value of 1 LSb of the Temperature Readout field in the Readout Register.

The SensorPath specification defines many different weights for the temperature LSb. The LM40 supports a

resolution of 0.5 ˚C and thus a value of 001 for this field. For a full definition of this field, please refer to the

SensorPath specification.

5-3

RO

Number of Bits. This field defines the total number of significant bits of the Temperature Readout field in the

Readout register. The total number of significant bits includes the number of bits representing the integer

part of the temperature data and the fractional part of it, as defined by the Resolution field. The LM40

supports 10-bits and thus a value of 001 for this field. For a full definition of this field please refer to the

SensorPath specification.

6RO

Sign (Signed Data). Defines the type of data in the Temperature Readout field of the Readout register.

0: Unsigned, positive fixed point value.

1: Signed, 2’s complement fixed point value. (value for the LM40)

7RO

RoutSize (Readout Register size). Defines the total size of the Readout register.

0: 16 bits. (value for the LM40)

8RO

IntSens (Internal Sensor Support). Indicates if the device supports internal temperature measurements, as

the LM40 does.

0: No internal temperature measurement

1: Internal temperature sensor implemented. (value for the LM40)

11-9

RO

# of Remotes (Number of Remote Sensors). Specifies the number of remote Temperature Sensors

supported by the function.

2: The number of Remote Temperature Sensors. (value for the LM40)

15-12

RO

Reserved. Will always read "0".

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