snap ethernet-based i/o units protocols and programming guide

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CHAPTER 2: OVERVIEW OF PROGRAMMING Using Digital Events and Reactions In a digital event, the brain monitors one or more inputs and outputs for a match to a specific pattern (the event). When the pattern is matched, the brain reacts in a predetermined way. You can configure up to 64 digital events and reactions (128 on a digital-only or a SNAP-UP1-M64 brain). See “Digital Events and Reactions—Read/Write” on page 127. Digital event/reactions can be as simple as turning on a light (reaction) when a door opens (event). They can also be very complex, depending on your needs. For example, suppose you need to monitor a critical group of switches. If switches 1, 2, and 3 are all off at once, you want to turn on an emergency light and sound an alarm. You can set up a digital event for the state of the three switches, and a reaction that automatically turns on the emergency light and alarm. The reaction to a digital event can turn digital points on or off and can also set bits in the Scratch Pad. The reaction can also depend on alarm conditions noted in the Scratch Pad. For instance, to regulate the temperature of a room, you might set up an alarm event that turns on a bit in the Scratch Pad when the temperature reaches 78° F (see “Using Alarms and Reactions” on page 31). Then you would set up a digital event/reaction to turn on an air conditioning unit when that Scratch Pad bit is on. NOTE: If you want to turn on or off digital points that are located on a different brain, you can do so by using the memory map copying feature when setting up event messages (see page 34). Digital Point and Scratch Pad Masks Both events and reactions are in the form of a mask. Digital point masks represent the 64 possible digital I/O points. Scratch Pad masks represent whatever you decide each bit should be. For each digital event/reaction, you set up eight masks, four for the event and four for the reaction: For the event: Digital points that must be on Digital points that must be off Scratch Pad bits that must be on Scratch Pad bits that must be off. For the reaction: Digital points that should be turned on Digital points that should be turned off Scratch Pad bits that should be turned on Scratch Pad bits that should be turned off. The masks work as a group. All the event masks must be a match for the brain to send the reaction. If it doesn’t matter whether a specific point or bit is on or off, leave its value at zero in both the on mask and the off mask. 30 SNAP Ethernet-Based I/O Units Protocols and Programming Guide
CHAPTER 2: OVERVIEW OF PROGRAMMING When you configure events and reactions, the masks are in hex notation. If you are setting up a Digital On mask for points 0–7, for example, you might do so as follows: Point number: 7 6 5 4 3 2 1 0 State: On -- On On -- -- -- On Binary notation: 1 0 1 1 0 0 0 1 Hex notation: B 1 For more information on mask data format, see page 41. You can also configure the brain to send a message as a reaction to digital events. See page 34. How Digital Events Trigger Reactions Reactions to digital events are level-triggered, not edge-triggered. The brain continually checks the digital state to see if it matches the event. The brain sends the reaction as soon as the state matches the event, and the brain continues to send the reaction until the state changes. If the state changes so that it no longer matches the event, the brain does NOT reverse the reaction. Digital Event/Reaction Example For example, suppose you have set up an event/reaction to turn on a light when a door is open. As soon as the event occurs (the door opens), the brain sends the reaction (turn on the light). Since the reaction is level-triggered, as long as the door remains open, the light will remain on. When the door is shut, the brain stops turning on the light, but it does NOT turn the light off. To turn off the light when the door is shut, you need to set up a second event/reaction. Suppose the input for the door’s status is on point 0, and the output for the light is on point 5. Here are the two event/reactions to turn on the light when the door is open, and turn off the light when the door is shut: Event #0: IF Point 0 (Door) is OFF (Open) Reaction #0: THEN Turn Point 5 (Light) ON Event #1: IF Point 0 (Door) is ON (Closed) Reaction #1: THEN Turn Point 5 (Light) OFF Using Alarms and Reactions A reaction can also be set up as a response to an alarm. You can configure alarms for analog points or digital counters. (See “Alarm Event Settings—Read/Write” on page 134). For example, you could monitor the pressure in a tank and set up an alarm if it rises above a certain level, or you could trigger an alarm when a specific number of boxes on a conveyor have passed through a beam sensor. For each alarm, you configure a suitable reaction. SNAP Ethernet-Based I/O Units Protocols and Programming Guide 31
Page 1 and 2: SNAP ETHERNET-BASED I/O UNITS PROTO
Page 3 and 4: Table of Contents Chapter 1: Introd
Page 5 and 6: Non-velocity Algorithms............
Page 7 and 8: Disconnecting......................
Page 9 and 10: Data Logging Configuration—Read/W
Page 11 and 12: Chapter 1 Introduction CHAPTER 1 We
Page 13 and 14: About this Guide CHAPTER 1: INTRODU
Page 15 and 16: For Help CHAPTER 1: INTRODUCTION If
Page 17 and 18: FEATURE CHAPTER 1: INTRODUCTION Ema
Page 19 and 20: CHAPTER 1: INTRODUCTION This task C
Page 21 and 22: CHAPTER 2 Chapter 2 Overview of Pro
Page 23 and 24: Referencing SNAP I/O Points CHAPTER
Page 25 and 26: Analog and Digital Systems (N Brain
Page 27 and 28: Digital-Only Systems The following
Page 29 and 30: I/O Point Types CHAPTER 2: OVERVIEW
Page 31 and 32: CHAPTER 2: OVERVIEW OF PROGRAMMING
Page 33 and 34: Watchdog (Digital and Analog Points
Page 39: CHAPTER 2: OVERVIEW OF PROGRAMMING
Page 45 and 46: Streaming Data CHAPTER 2: OVERVIEW
Page 47 and 48: Logging Data Area Number of Bytes I
Page 49 and 50: Using PID Loops What is a PID? CHAP
Page 51 and 52: Equations Common to All Algorithms
Page 55 and 56: CHAPTER 3 Chapter 3 Using the SNAP
Page 57 and 58: CHAPTER 3: USING THE SNAP ETHERNET
Page 63 and 64: Environment Visual Basic 6 Internet
Page 65 and 66: MemMap Example Code CHAPTER 3: USIN
Page 71 and 72: Return Values CHAPTER 3: USING THE
Page 73 and 74: IsOpenDone V Close V Return Values
Page 75 and 76: Digital Point Methods CHAPTER 3: US
Page 77 and 78: SetDigBankOnMask V [in] long nPts63
Page 79 and 80: Analog Bank Methods CHAPTER 3: USIN
Page 81 and 82: GetStatusWatchdogTime [out] long pn
Page 87 and 88: GetLastStreamStandardBlock (ActiveX
Page 89 and 90: CHAPTER 4 Chapter 4 Using the IEEE
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CHAPTER 4: USING THE IEEE 1394-BASE
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Bytes 0-3 Bytes 4-7 Bytes 8-11 Byte
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Bytes 0-3 Bytes 4-7 Bytes 8-11 The
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Bytes 0-3 Bytes 4-7 Bytes 8-11 Byte
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Read and clear latches for individu
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Scaling CHAPTER 4: USING THE IEEE 1
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Read and Write Packet Structure Par
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CHAPTER 5 Chapter 5 Advanced Modbus
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CHAPTER 5: ADVANCED MODBUS PROGRAMM
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APPENDIX A Appendix A SNAP Ethernet
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Status Area Read—Read Only This i
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Date and Time Configuration—Read/
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Security Configuration—Read/Write
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Serial Module Configuration—Read/
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Wiegand Serial Module Configuration
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SNMP Configuration—Read/Write (Do
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Starting Address Length Type Descri
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Digital Point Read—Read Only NOTE
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Analog Point Read—Read Only See
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Analog and Digital Point Configurat
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Digital Events and Reactions—Read
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Analog Point Calculation and Set—
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Analog Read and Clear/Restart—Rea
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Serial Event Configuration—Read/W
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Data Log—Read/Write (Does not app
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Appendix B Table of Offsets Introdu
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Module Point (Decimal) Point (Hex)
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Index A access, setting up SNMP sec
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error codes IEEE 1394-based protoco
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O off-latch, 20 offset, 24 IEEE 139
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