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

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CHAPTER 2: OVERVIEW OF PROGRAMMING For analog points, alarms are based on the analog input value. For digital points, alarms are based on the counter value. For each point, you can configure any or all of the following alarms: Deviation alarm—sets a range on either side of the current value that is acceptable; beyond that range, the reaction occurs. For example, suppose you are monitoring temperature. If the current value is 80 and you set a deviation limit of 6, the reaction will not occur unless the value drops below 74 or rises above 86. NOTE: When a reaction occurs, the deviation limit stays the same, but the value that set off the reaction becomes the new deviation value. In this example, if the temperature drops to 73, the reaction occurs. Six is still the deviation limit, but now 73 is the deviation value; another reaction will not occur unless the value drops below 67 or rises above 79. High-limit alarm—sets a fixed upper limit. If the analog value or counter is higher than the high limit, the reaction occurs. Low-limit alarm—sets a fixed lower limit. If the analog value or counter is lower than the low limit, the reaction occurs. How Alarms Trigger Reactions Reactions to alarms are edge-triggered, not level-triggered, and when the alarm state changes, the reaction is automatically reversed. The brain sends the reaction just once, as soon as the alarm occurs (at the “edge” of the alarm). The brain does not send the reaction again until the alarm occurs again. If the alarm stops, however, the brain reverses the reaction. For example, suppose you set up a high-limit alarm that turns on a Scratch Pad bit that will turn on a fan if the temperature goes over 70°. As soon as the alarm state occurs (the temperature goes over 70°), the brain sends the reaction (turns on the bit to turn on the fan). If the temperature remains above 70°, the brain does not continue to turn on the fan bit; the bit just stays on. When the temperature falls back below the high limit (70° minus whatever deadband you have set), the brain automatically reverses the reaction by turning the Scratch Pad bit off. (To turn the fan off, you would have to set up a reaction for the off bit, turning the fan off.) Notice that the reaction and its reversal are absolute; they do not depend on the pre-alarm condition. For example, if the bit to turn on the fan was already on at the time the temperature rose above 70°, the reaction would turn the bit on even though it was already on. When the temperature fell back below 70°, the brain would not return the fan bit to its pre-alarm condition (on); it would turn the bit off. Using Serial Events and Reactions If you are using Opto 22 serial communication modules with a SNAP Ultimate or SNAP Ethernet I/O unit, you can configure a serial event to send a serial message, to send an SNMP trap, or to turn bits in the Scratch Pad on or off when a specific string is received from one or more modules. See “Serial Event Configuration—Read/Write” on page 139 or “Wiegand Serial Event Configuration—Read/Write” on page 140. 32 SNAP Ethernet-Based I/O Units Protocols and Programming Guide
CHAPTER 2: OVERVIEW OF PROGRAMMING Before you configure serial events and reactions, make sure you have configured the serial modules. (See page 111 or page 113.) Using Timers Reactions normally occur immediately after their events happen. If you want a delay between an event and its reaction, you can configure a timer. See . The timer starts timing in response to a digital event or a Scratch Pad bit pattern (or both), waits the length of time you set, and then sets off a digital reaction and/or sets a different Scratch Pad pattern. Using SNMP in Reactions To send an SNMP trap as a reaction to an event, you must also tell the brain information about the SNMP agent and access privileges for hosts on the network. SNMP Access Privileges Community groups control access to information from the SNAP Ethernet-based brain. The first community group, public, is set up for you. All hosts on the network are part of the public group; all can read and write brain data, but cannot receive traps. You can change or delete this public group if necessary. In order to receive traps, a host must be a registered management host and be part of a community group that does have access privileges for traps. Once a registered management host becomes part of a community group, that group is no longer available to non-registered hosts. It includes only the hosts registered to it. You must set up the additional community groups you need, either in ioManager or in your program. See “SNMP Configuration—Read/Write” on page 115. SNMP Traps The SNAP Ethernet-based brain can send three kinds of traps: Authentication trap—sent when a host requests data that is outside its access permissions Cold start trap—sent whenever the brain is turned on Exception trap—sent in reaction to an event; an exception trap is a type of event message. Authentication and cold start traps require no configuration and can simply be enabled. Exception traps must be configured when you set up event messages. SNAP Ethernet-Based I/O Units Protocols and Programming Guide 33
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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 41: 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
Page 91 and 92: 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 4: USING THE IEEE 1394-BASE
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CHAPTER 4: USING THE IEEE 1394-BASE
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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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