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| Quantum Ethernet TCP/IP Modbus Application Protocol |
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| Example | Modbus Application Protocol PDU | |
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| Here are the values for a sample mbap_pdu for reading a register: | |
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| 00 01 00 00 00 06 01 03 00 00 00 01 |
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| This example has the folowing structure and content: | |
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| inv_id 00 01 |
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| proto_id | 00 00 |
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| len | 00 00 |
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| dst_idx | 01 |
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| func_code03 | |
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| data | 00 00 00 01 |
C.1.2 | Modbus Application Protocol Service Classes | ||
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| There are several classes of service that are part of the Modbus Application | |
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| Protocol. They include: | |
Data access | Read/write both discrete and analog data values from PLC register files. | ||
Online | Services make relatively minor alterations to ladder logic programs with a highly | ||
programming | controlled introduction of these changes into the executing program. | ||
Image download/ | Image download services support the downloading of a ladder logic control | ||
upload | program to the PLC. Image upload services support the uploading of a ladder logic | ||
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| control program from a PLC to PC host for archival/backup purposes. | |
Configuration | Configuration services allow the user to define parameter values which affect the | ||
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| PLC’s register files, I/O map, communication port configuration and scan attributes, | |
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| to name a few. |
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Device execution | The class of service allows the user to start/stop the PLC scan execution. These | ||
state control | services require the user to be in an application login context which is obtained | ||
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| through other Modbus services. | |
840 USE 115 00 Version 1.0 | 79 |
