安全系统控制与MAXQ2000-Security Syste

文章摘要：Abstract: Alarm control panels are a part of almost everyone's daily life, either at home or at work. This article describes a sample alarm control application using the MAXQ2000 Low-Power LCD Microcontroller, created with the MAX-IDE development environment. The MAXQ2000 can be easily interface

安全系统控制与MAXQ2000-Security Syste,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com
Abstract: Alarm control panels are a part of almost everyone's daily life, either at home or at work. This article describes a sample alarm control application using the MAXQ2000 Low-Power LCD Microcontroller, created with the MAX-IDE development environment. The MAXQ2000 can be easily interfaced to peripherals typically used in security applications, including LCD displays, PIN entry keypads, piezoelectric horns and buzzers, and magnetic reed switches.

Common alarm-control panels contain several input devices and require user displays. The usual components for these systems include:

• A device to accept input from the user: a 4 x 4 switch keypad.
• A device to display output to the user: an LCD display.
• An input device: a magnetic reed switch.
• An output device: a piezoelectric horn.

These several components can be managed and controlled by a simple application and the powerful, flexible MAXQ2000 microcontroller. This application, available for download, was written in MAXQ assembly language using the MAX-IDE development environment. The code was targeted for the MAXQ2000 evaluation kit board, using the following additional hardware:

• Keypad: Grayhill 16-button (4 rows by 4 columns) keypad 96BB2-006-F
• Piezoelectric horn: CEP-1172
• Magnetic reed switch: standard single-loop type

Design Goals

Our example application performs the following tasks:

• Monitors the magnetic reed switch to determine if a door/window is open or closed.
• Allows the user to arm or disarm the system by entering a PIN on the keypad.
• Displays status information to the user on the LCD.
• Provides audio indications of keypresses and sensor open/close events by sounding the piezoelectric horn.
• Sounds the horn continuously if the sensor is opened while the system is armed. The behavior of the alarm control application consists of four discrete states: CLOSED, OPEN, SET, and ALERT (Figure 1).

Figure 1. The alarm control application operates in four main states: CLOSED, OPEN, SET, AND ALERT.

Interfacing to the Magnetic Reed Switch

In an alarm system, magnetic reed switches are installed in two parts: a magnet and the actual reed switch. The magnet portion is placed on the moving section of a door or window, while the switch portion is placed on the frame. When the door or window is closed, the magnet closes the reed switch, indicating a nonalarming condition. If the system is armed and the window or door is opened, the reed switch changes state, allowing the MAXQ2000 to sound an intrusion alert.

The reed switch is interfaced to the MAXQ2000 simply by connecting it between port pins P5.2 and P5.3. With P5.2 set to an active-low pulldown (PD = 1, PO = 0) and P5.3 set to a weak pullup input (PD = 0, PO = 1), P5.3 will read zero when the reed switch is closed and one when the reed switch is open.

   move    PD5.2, #1         ; Drive one side of reed switch LOW
   move    PO5.2, #0

   move    PD5.3, #0         ; Set weak pullup high on other side
   move    PO5.3, #1

...

ML_Closed_Check:
   move    C, PI5.3
   jump    NC, ML_Closed_L   ; Switch is closed, continue in this state

   call    ShortBeep
   call    ShortPause
   call    ShortBeep
   call    ShortPause
   call    ShortBeep
   call    ShortPause
   call    ShortBeep
   call    ShortPause
   jump    ML_Open           ; Switch is open, transition to OPEN state

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