Rainbow Electronics LM41 - Manual (Page 19)

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 LM41 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
LM41 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 LM41).
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 0349h
Reserved # of Remotes
Int
Sens
Rout
Size
Sign 10-Bits
0.5˚C
Resolution
0 0 0 0 0 0 1 1 0 1 0 0 1 0 0 1
This register defines the format of the temperature data in the readout register. The LM41 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 LM41 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 LM41
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.
6 RO 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 LM41)
7 RO RoutSize (Readout Register size). Defines the total size of the Readout register.
0: 16 bits. (value for the LM41)
8 RO IntSens (Internal Sensor Support). Indicates if the device supports internal temperature measurements, as
the LM41 does.
0: No internal temperature measurement
1: Internal temperature sensor implemented. (value for the LM41)
11-9 RO # of Remotes (Number of Remote Sensors). Specifies the number of remote Temperature Sensors
supported by the function.
1: The number of Remote Temperature Sensors. (value for the LM41)
15-12 RO Reserved. Will always read "0".
LM41
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