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| 型号： | LM89EVAL |
| 厂商： | National Semiconductor |
| 文件页数： | 9/32页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION LM89 |
| 标准包装： | 1 |
| 传感器类型： | 温度 |
| 传感范围： | 0°C ~ 125°C |
| 接口： | SMBus（2 线/I²C） |
| 灵敏度： | ±1°C |
| 电源电压： | 3 V ~ 3.6 V |
| 嵌入式： | 否 |
| 已供物品： | 板，CD |
| 已用 IC / 零件： | LM89 |
| 相关产品： | LM89CIM-ND - IC TEMP SENSOR DGTL 8-SOIC LM89CIMX-ND - IC TEMP SENSOR DGTL 8-SOIC LM89CIMM-ND - IC TEMP SENSOR DGTL 8-MSOP LM89CIMMX-ND - IC TEMP SENSOR DGTL 8-MSOP |
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SNIS128C – AUGUST 2002 – REVISED MARCH 2013
THE ALERT OUTPUT
The LM89's ALERT pin is an active-low open-drain output that is triggered by a temperature conversion that is
outside the limits defined by the temperature setpoint registers. Reset of the ALERT output is dependent upon
the selected method of use. The LM89's ALERT pin is versatile and will accommodate three different methods of
use to best serve the system designer: as a temperature comparator, as a temperature based interrupt flag, and
as part of an SMBus ALERT system. The three methods of use are further described below. The ALERT and
interrupt methods are different only in how the user interacts with the LM89.
Each temperature reading (LT and RT) is associated with a T_CRIT setpoint register (LCS, RCS), a HIGH
setpoint register (LHS and RHS) and a LOW setpoint register (LLS and RLS). At the end of every temperature
reading, a digital comparison determines whether that reading is above its HIGH or T_CRIT setpoint or below its
LOW setpoint. If so, the corresponding bit in the STATUS REGISTER is set. If the ALERT mask bit is not high,
any bit set in the STATUS REGISTER, with the exception of Busy (D7) and OPEN (D2), will cause the ALERT
output to be pulled low. Any temperature conversion that is out of the limits defined by the temperature setpoint
registers will trigger an ALERT. Additionally, the ALERT mask bit in the Configuration register must be cleared to
trigger an ALERT in all modes.
ALERT Output as a Temperature Comparator
When the LM89 is implemented in a system in which it is not serviced by an interrupt routine, the ALERT output
could be used as a temperature comparator. Under this method of use, once the condition that triggered the
ALERT to go low is no longer present, the ALERT is de-asserted ( Figure 4 ). For example, if the ALERT output
was activated by the comparison of LT > LHS, when this condition is no longer true the ALERT will return HIGH.
This mode allows operation without software intervention, once all registers are configured during set-up. In order
for the ALERT to be used as a temperature comparator, bit D0 (the ALERT configure bit) in the FILTER and
ALERT CONFIGURE REGISTER (xBF) must be set high. This is not the power-on-default state.
Remote High Limit
RDTS Measurement
LM89 ALERT Pin
Status Register: RTDS High
TIME
Figure 4. ALERT Comparator Temperature Response Diagram
ALERT Output as an Interrupt
The LM89's ALERT output can be implemented as a simple interrupt signal when it is used to trigger an interrupt
service routine. In such systems it is undesirable for the interrupt flag to repeatedly trigger during or before the
interrupt service routine has been completed. Under this method of operation, during a read of the STATUS
REGISTER the LM89 will set the ALERT mask bit (D7 of the Configuration register) if any bit in the STATUS
REGISTER is set, with the exception of Busy (D7) and OPEN (D2). This prevents further ALERT triggering until
the master has reset the ALERT mask bit, at the end of the interrupt service routine. The STATUS REGISTER
bits are cleared only upon a read command from the master (see Figure 5 ) and will be re-asserted at the end of
the next conversion if the triggering condition(s) persist(s). In order for the ALERT to be used as a dedicated
interrupt signal, bit D0 (the ALERT configure bit) in the FILTER and ALERT CONFIGURE REGISTER (xBF) must
be set low. This is the power-on-default state.
The following sequence describes the response of a system that uses the ALERT output pin as a interrupt flag:
1. Master Senses ALERT low
2. Master reads the LM89 STATUS REGISTER to determine what caused the ALERT
Copyright ? 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM89
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