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參數(shù)資料
| 型號(hào)： | LM78 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Microprocessor System Hardware Monitor |
| 中文描述： | 微處理器系統(tǒng)硬件監(jiān)視器 |
| 文件頁數(shù)： | 20/31頁 |
| 文件大小： | 424K |
| 代理商： | LM78 |
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Functional Description
(Continued)
7.0 TEMPERATURE MEASUREMENT SYSTEM
The LM78 bandgap type temperature sensor and ADC per-
form 8-bit two’s-complement conversions of the tempera-
ture. A digital comparator is also incorporated that compares
the readings to the user-programmable Overtemperature
setpoint and Hysteresis values.
7.1 Temperature Data Format
Temperature data can be read from the Temperature, T
OI
Set
Point, and T
HYST
Set Point registers; and written to the T
OI
Set Point, and T
HYST
Set Point registers. Temperature data
is represented by an 8-bit, two’s complement word with an
LSB (Least Significant Bit) equal to 1.0C:
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
+1.0C
+0C
1.0C
25C
55C
7.2 Temperature Interrupts
The normal mode for temperature interrupts in the LM78 is
an “Interrupt”mode operating in the following way: Exceeding
T
causes an interrupt that will remain active indefinitely
until reset by reading Interrupt Status Register 1. Once an
interrupt event has occurred by crossing T
, then reset, an
interrupt will only occur again by the temperature going
below T
. Again, it will remain active indefinitely until
being reset by reading Interrupt Status Register 1.
A “Comparator” mode for temperature interrupts can be
made available by setting the T
limit to 127C. This
results in a simple “thermostat” type of function where an
interrupt will be set whenever the temperature exceeds the
T
OI
limit. Reading Interrupt Status Register 1 will clear the
interrupt as usual, but the interrupt will set again after the
completion of another measurement cycle. It will remain set
until the temperature goes below the T
OI
limit (allow up to
two measurement cycles for clearing after descending below
T
OI
while in Comparator mode).
DS012873-18
FIGURE 10. Temperature-to-Digital Transfer Function
(Non-Linear Scale for Clarity)
DS012873-19
*
Note:
Interrupt resets occur only when interrupt Status Register 1 is read.
(a) Interrupt Mode
DS012873-20
Interrupt resets occur when Interrupt Status Register 1 is read but will set
again when monitoring cycle continues (as long as temperature exceeds
T
). When temperature descends below T
allow up to two monitoring
loops before the Temperature Interrupt resets.
(b) Comparator Mode
FIGURE 11. Temperature Interrupt Response Diagram
L
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