lm95172qa2 National Semiconductor Corporation, lm95172qa2 Datasheet - Page 16

• Manufacturer Part Number: lm95172qa2
• Description: 13-bit To 16-bit Digital Temperature Sensor With 3-wire Interface
• Manufacturer: National Semiconductor Corporation

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1.7 INTERNAL REGISTER STRUCTURE
The LM95172QA2 MDA has four registers that are accessible by issuing a command byte (a R/W Bit plus the register address:
Control/Status, T
See Section 1.4, "Communicating with the LM95172QA2 MDA", for a complete description of the serial communication protocol.
The following diagram describes the Command Byte and lists the addresses of the various registers. On power-up, the Command
Byte will point to the Temperature Register by default. The temperature is read by lowering the CS line and then reading the 16-
Bit temperature register; all other registers are accessed by writing a Command Byte after reading the temperature.
All registers can be communicated with, either in Continuous Conversion mode or in Shutdown mode. When the
LM95172QA2 MDA has been placed in Shutdown Mode, the Temperature register will contain the temperature data which resulted
from the last temperature conversion (whether it was the result of a continuous-conversion reading or a one-shot reading).
1.7.1 Command Byte
Bit <7> Read/Write Bit. Tells the LM95172QA2 MDA if the host will be writing to, or reading from, the register to which this byte is
pointing.
Bits <6:3> Not Used. These Bits must be zero. If an illegal address is written, the LM95172QA2 MDA will return 0000h on the
subsequent read.
Bits <2:0> Pointer Address Bits. Points to desired register. See table below.
Power-On Reset state: 00h
Reset Conditions: Upon Power-on Reset
1.7.2 Temperature Register
(Read Only): Default Register
Bit <15:1>: Temperature Data Byte. Reperesents the temperature that was measured by the most recent temperature conversion
in two's complement form. On power-up, this data is invalid until the DAV Bit in the Control/Status Register is high (that is, after
completion of the first conversion).
The resolution is user-programmable from 13-Bit resolution (0.0625°C) through 16-Bit resolution (0.0078125°C). The desired res-
olution is programmed through Bits 4 and 5 of the Control/Status Register. See the description of the Control/Status Register for
details on resolution selection.
The Bits not used for a selected resolution are always set to "0" and are not to be considered part of a valid temperature reading.
For example, for 14-Bit resolution, Bit <1> is not used and, therefore, it is invalid and is always zero.
Bit <0>: Conversion Toggle or, if 16-Bit resolution has been selected, this is the 16-Bit temperature LSB.
When in 13-Bit, 14-Bit, or 15-Bit resolution mode, this Bit toggles each time the Temperature register is read if a conversion has
completed since the last read. If conversion has not completed, the value will be the same as the last read.
1°C
D7
HIGH
0.5°C
D6
, T
LOW
0.25°C
, and Identification. Which of these registers will be read or written is determined by the Command Byte.
Sign
D15
D5
R/W
P7
128°C
0.125°C
D14
D4
P2
0
0
0
0
1
1
1
1
P6
0
64°C
D13
0.0625°C
P5
P1
0
0
0
1
1
0
0
1
1
D3
32°C
D12
P4
0
P0
0
1
0
1
0
1
0
1
0.03125°C
16
D2
16°C
P3
D11
0
Invalid. (Note 3)
Invalid. (Note 3)
Control/Status
Identification
Register
P2
0.015625°C
T
T
Register Select
D10
8°C
HIGH
LOW
D1
P1
4°C
D9
P0
Conversion - Toggle/
2°C
D8
0.0078125°C
D0