viii D320 PLC User's Manual
Chapter 7: Testing And Troubleshooting 127
Test Precautions................................................................................................................................................. 128
System Checks................................................................................................................................................... 128
Testing Procedures............................................................................................................................................. 130
Correcting Errors ............................................................................................................................................... 132
System Check ............................................................................................................................................ 132
Power Supply Check.................................................................................................................................. 133
Run Check ................................................................................................................................................. 134
Error Check................................................................................................................................................ 135
I/O Check................................................................................................................................................... 136
Troubleshooting, Maintenance and Inspection Tables....................................................................................... 138
Periodic Inspection and Preventive Maintenance ...................................................................................... 141
Chapter 8: Troubleshooting Noise Problems 143
Noise Occurrence............................................................................................................................................... 144
Types of Noise........................................................................................................................................... 144
Electrical Noise Fundamental Definitions ................................................................................................. 144
Sources of Noise ........................................................................................................................................ 145
Advised Installation Practices............................................................................................................................ 146
Shield the PLC........................................................................................................................................... 146
Proper Cable Selection .............................................................................................................................. 146
Ground the PLC......................................................................................................................................... 146
Isolation and Filtering Techniques..................................................................................................................... 147
Isolation ..................................................................................................................................................... 147
Filters......................................................................................................................................................... 148
Methods of Handling Large Voltage Spikes Such as Lightning........................................................................ 149
Surge Absorber .......................................................................................................................................... 149
Burying Wire ............................................................................................................................................. 149
Shielding Cabling .............................................................................................................................................. 150
Methods to Handle I/O Inductive Loads............................................................................................................ 151
Warning ............................................................................................................................................................. 153
Troubleshooting................................................................................................................................................. 154
Appendix A: D50 PLC Communication Protocol 155
Communication Rules ....................................................................................................................................... 156
Communication Environment.................................................................................................................... 156
Communication Protocol................................................................................................................................... 156
Step 1
Query (Q)..................................................................................................................................... 156
Step 2
Query Acknowledge (QA)........................................................................................................... 156
Step 3
Response Request (RR) ............................................................................................................... 156
Step 4
Response (R)................................................................................................................................ 156
Step 5
Repeated Response ...................................................................................................................... 157
Communications Delay.............................................................................................................................. 157
Example..................................................................................................................................................... 157
CPU ID ...................................................................................................................................................... 158
Function Codes Included in the Query ...................................................................................................... 158
Cyclic Redundancy Checking (CRC) ........................................................................................................ 159
The Structure of the Communications Frame .................................................................................................... 160
Read Bits.................................................................................................................................................... 161
Write Bits................................................................................................................................................... 162
Read Words ............................................................................................................................................... 163
Write Words .............................................................................................................................................. 164
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