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參數(shù)資料
| 型號： | LM84 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | Diode Input Digital Temperature Sensor with Two-Wire Interface |
| 中文描述： | 二極管輸入數(shù)字溫度傳感器兩線接口 |
| 文件頁數(shù)： | 10/16頁 |
| 文件大?。?/td> | 168K |
| 代理商： | LM84 |
1.0 Functional Description
(Continued)
1.3 SMBus INTERFACE
The LM84 operates as a slave on the SMBus, so the
SMBCLK line is an input (no clock is generated by the LM84)
and the SMBData line is bi-directional. According to SMBus
specifications, the LM84 has a 7-bit slave address. Bit 4 (A3)
of the slave address is hard wired inside the LM84 to a 1.
The remainder of the address bits are controlled by the
address select pins ADD1 and ADD0, and are set by con-
necting these pins to ground for a low, (0) , to V
CC
for a high,
(1), or left floating (TRI-LEVEL).
Therefore, the complete slave address is:
A6
MSB
and is selected as follows:
A5
A4
A3
A2
A1
A0
LSB
Address Select Pin State
LM84 SMBus
Slave Address
A6:A0 binary
001 1000
001 1001
001 1010
010 1001
010 1010
010 1011
100 1100
100 1101
100 1110
ADD0
0
0
0
TRI-LEVEL
TRI-LEVEL
TRI-LEVEL
1
1
1
The LM84 latches the state of the address select pins during
the first read or write on the SMBus. Changing the state of
the address select pins after the first read or write to any
device on the SMBus will not change the slave address of
the LM84.
ADD1
0
TRI-LEVEL
1
0
TRI-LEVEL
1
0
TRI-LEVEL
1
1.4 TEMPERATURE DATA FORMAT
Temperature data can be read from the Local Temperature,
Remote Temperature, and T_CRIT setpoint registers. Tem-
perature data can only be written to the T_CRIT setpoint
registers. Temperature data is represented by an 8-bit, two’s
complement byte with an LSB (Least Significant Bit) equal to
1C:
Temperature
Digital Output
Binary
0111 1101
0001 1001
0000 0001
0000 0000
1111 1111
1110 0111
1100 1001
Hex
7Dh
19h
01h
00h
FFh
E7h
C9h
+125C
+25C
+1C
0C
1C
25C
55C
1.5 OPEN-DRAIN OUTPUTS
SMBData and T_CRIT_A outputs are open-drain and do not
have internal pull-ups. A “high” level will not be observed on
these pins until pull-up current is provided from some exter-
nal source, typically a pull-up resistor. Choice of resistor
value depends on many system factors but, in general, the
pull-up resistor should be as large as possible. This will
minimize any local temperature reading errors due to self
heating of the LM84. The maximum resistance of the pull-up,
based on LM84 specification for High Level Output Current,
to provide a 2V high level, is 30 k
.
1.6 DIODE FAULT DETECTION
Before each remote conversion the LM84 goes through an
external diode fault detection sequence. If the D+ input is
shorted to V
or floating then the temperature reading will
be +127C, bit 2 (OPEN) of the Status Register will be set. If
the Remote T_CRIT setpoint is set to less than +127C then
bit 4 (RTCRIT) of the Status Register will be set which will
activate the T_CRIT_A output, if enabled. If D+ is shorted to
GND or D, the temperature reading will be 0C and bit 2 of
the Status Register will not be set.
L
www.national.com
10
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