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LM40 Fiches technique(PDF) 19 Page - National Semiconductor (TI) |
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LM40 Fiches technique(HTML) 19 Page - National Semiconductor (TI) |
19 / 27 page 2.0 Register Set (Continued) 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". www.national.com 19 |
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