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Choosing Communication
Chapter 5
5-4
Nodes
Nodes affect transmission time in the following ways:
During one complete token rotation, each node on the DH+ link
receives the token whether or not it has something to send.
Each node spends from 1.5 ms (if it has no messages to send) to 38 ms
(maximum time allotted) with the token, assuming there are no retries
(Figure 5.2).
Figure 5.2
Token
Passing
Station
Station
Station
Station
Station
DH+ link
Max. 38 ms
with the token
Min.
1.5 ms
with
the token
1
2
3
4
5
Size and Number of Messages
A PLC-5 processor encodes messages into packets for transmission on the
DH+ link. The maximum number of data words in a packet depends on
the sending station and command type. This limit comes from the network
protocol, which limits a station to transmitting a maximum of 271 bytes
per token pass. A station can send more than one message in a token pass,
provided that the total number of combined command and data bytes does
not exceed 271.
If a message exceeds the maximum packet size allotted, however, the
sending station will require more than one token pass to complete the
message. For example, if a PLC-5 processor wants to send a 150-word
message, it will have to transmit two messages, possibly requiring many
token rotations.
The number of messages a station has to send also affects throughput time.
For example, if a station has three messages queued and a fourth is
enabled, the fourth message may have to wait until the previous three
are processed.
- Classic 1785 PLC5 1
- Programmable 1
- Controllers 1
- AllenBradley 1
- Important User Information 2
- Summary of Changes 3
- Table of Contents 4
- Table of Contentsii 5
- Table of Contents iii 6
- Table of Contentsiv 7
- of this Manual 8
- Manual Organization 9
- How to Use this Manual 9
- Understanding Your System 11
- Designing 12
- Systems 12
- Preparing 13
- Functional Specification 13
- Figure 1.2 14
- ProgramDevelopment 14
- Introducing 15
- Classic PLC5 15
- Processor Modules 15
- Using the Classic PLC5 18
- Processor as a Remote I/O 18
- Choosing Hardware 20
- Selecting I/O Module Density 21
- Master/Expander I/O Modules 22
- Selecting I/O Adapter 23
- Other Devices on an I/O Link 24
- Selecting 25
- I/O Chassis 25
- Selecting an Operator 25
- Interface 25
- Other Operator Interfaces 27
- Choosing 28
- a Classic PLC5 28
- Processor for Your 28
- Application 28
- Selecting Power Supplies 28
- Chapter 2 29
- Powering 30
- Table 2.K 30
- 1770XY is a 3.6 V 32
- a PLC5 Processor 33
- Backup System 33
- Selecting Link Terminators 34
- Connecting a 34
- Programming Terminal to a 34
- Processor Module 34
- Choosing Cables 34
- Programming Terminal 35
- Placing System Hardware 36
- Chapter 3 37
- Planning Cabling 40
- Laying Out the 41
- Backpanel Spacing 41
- Grounding Configuration 42
- Assigning Addressing Modes 43
- Racks, and Groups 43
- Understanding the Terms 44
- Used in this Chapter 44
- Choosing the 45
- Addressing Mode 45
- Using 1Slot Addressing 48
- Chapter 4 49
- Using 1/2Slot Addressing 50
- Assigning 51
- Remote I/O Racks 52
- Addressing 54
- Choosing Communication 59
- Chapter 5 60
- Figure 5.1 60
- Front Panels 60
- Configuring Communication 61
- Configuring a DH+ Link 61
- Figure 5.2 62
- Passing 62
- Test Setup 65
- Application Guidelines 66
- Connecting a DH+ Link 68
- Choosing Programming 68
- Terminal Connection 68
- Remote Connection 69
- Serial Connections 70
- 1770KF2/B 71
- Planning Your System Programs 72
- Deciding How to Use an SFC 73
- Preparing the Programs 74
- Organizing a Machine Example 75
- Addressing Data T 78
- is the default file number 79
- the Processor 80
- Status File 80
- Chapter 6 81
- Table 6.F 81
- Status File Addresses 81
- Selecting Interrupt Routines 83
- Program Execution States 84
- Writing a Fault Routine 85
- Major Fault Codes 86
- Chapter 7 87
- Table 7.H 87
- Fault Codes 87
- Programming a Fault Routine 88
- Figure 7.4 89
- Testing a Fault Routine 90
- Setting Up a Fault Routine 90
- Enabling a Fault Routine 90
- Figure 7.5 91
- Setting PowerUp Protection 92
- Understanding 93
- ProcessorDetected 93
- Major Faults 93
- Fault in a Remote I/O Chassis 94
- Rack Fault 94
- Objectives 96
- Transferring Data Using 96
- Adapter Mode 96
- Discrete 99
- Chapter 8 101
- Table 8.K 101
- Programming Block 102
- Transfer in Adapter Mode 102
- Addressing Tips 103
- Figure 8.6 106
- Figure 8.7 107
- Figure 8.8 108
- Figure 8.9 109
- Transferring Data 111
- Using Scanner Mode 111
- Programming Discrete 111
- Transfer in Scanner Mode 111
- BlockTransfer Sequence 114
- Programming 116
- Considerations 116
- Calculating Program Timing 118
- Chapter 9 119
- I/O Scanning 120
- I/O ScanningDiscrete 122
- Figure 9.2 123
- Transferring 123
- Instruction Timing and 124
- Memory Requirements 124
- Processors 125
- File Instructions 128
- Program Constants 130
- Direct and Indirect Elements 130
- Maximizing System Performance 133
- Backplane T 134
- Remote I/O Scan T 134
- Number of Rack Entries 135
- Block Transfers 135
- Calculating 136
- Processor 138
- Calculating Throughput 138
- Selecting Switch Settings 139
- Chassis Backplane with 140
- Adapter Module 140
- Chassis Configuration Plug 141
- Remote I/O Adapter Module 142
- 1771ASB Series C without 142
- Complementary I/O 142
- Appendix A 143
- 1771ASB Series C with 144
- AdapterMode 146
- ProcessorsSW2 146
- PLC5 or Scanner Module 146
- PLC2/20, 2/30, or Sub I/O 147
- Scanner Module System 147
- PLC3 or PLC5/250 System 148
- Design Worksheets 151
- Appendix B 152
- Determine Control Strategy 154
- Identify Chassis Locations 156
- Total I/O Module Requirements 159
- Assign Addresses 160
- Select Adapter Modules 162
- Place System Hardware 164
- Configure Switch Settings 165
- Select Power Supplies 173
- Choose a Programming Terminal 174
- Select Operator Interface 176
- With major offices worldwide 186
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