It is possible to read and send data with TComPort for modbus RTU protocol?
I have read wiki http://en.wikipedia.org/wiki/Modbus for modbus, but what mean start and end with 3.5c idle?
I use C++Builder2009
Share
Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
It is possible to read and send data with TComPort for modbus RTU protocol?
I have read wiki http://en.wikipedia.org/wiki/Modbus for modbus, but what mean start and end with 3.5c idle?
I use C++Builder2009
Of course it’s possible.
In MODBUS ASCII it is easy to determine end of message since 2 bytes are used for single byte transmitted over communication line (byte is transmitted as it’s ASCII hexadecimal representation), but in MODBUS RTU you have 1 byte used for single byte transmitted which means that they had to know somehow that messages has ended. So, bytes are added to a new message as long as pause between them is less then 3.5 characters. When pause is greater then 3.5, you have an end of a message and you can parse the message, process it, and get ready for new one. This idle time is measured in characters since that is the only constant. Time period of 1 character transmitted over 9600 and over 115200 is not the same, and it is also not the same for 9600-8N1 and for 9600-8E2, so you have to adjust that time based on COM port settings.