Serial Communications Protocol Specifications - Swissvacuum.com
Serial Communications Protocol Specifications - Swissvacuum.com
Serial Communications Protocol Specifications - Swissvacuum.com
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CODE EXAMPLES<br />
- 14 -<br />
In this section we show how to <strong>com</strong>pute the CRC according to the Modbus protocol requirements. Note that the CRC<br />
must be added to the packet to be sent to the controller and also must be <strong>com</strong>puted on the received packet to verify<br />
its integrity.<br />
Also some little programs are reported on how to prepare a query packet to talk to the controller using C language<br />
and Visual Basic.<br />
QUERY<br />
ANSWER<br />
Prepare data packet<br />
CRC calculation<br />
Add CRC at the end of<br />
data packet<br />
Get the answer from the<br />
serial port buffer<br />
CRC calculation on the<br />
received packet<br />
Compare the <strong>com</strong>puted<br />
CRC calcolato with the<br />
CRC in the data packet<br />
No match: data packet<br />
corrupted: do not use it!<br />
Fig. 6 – CRC calculation<br />
Send packet<br />
Receiving a data packet<br />
CRCs match: data packet<br />
correct: decode it!<br />
Warning! All examples are only suggestions and indications of a possible program organization.<br />
ANGELANTONI Industrie declaims all responsibility for the use (correct or not correct) of this<br />
code.<br />
It is up to the software engineer to modify, <strong>com</strong>plete and test the examples for his own purposes.<br />
<strong>Serial</strong> <strong>com</strong>munications protocol vers. 2.02 Angelantoni Industrie Spa Massa Martana (PG) Italy
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