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Hi all,
after a long time. this problem is somewhat related to VB. I am writing code for comm between VB and microcontroller. thru RS232. I use Modbus protocol. but it has limitation of 256 bytes. I have to send 2MB data. So i want to know is there any protocol for that or i have to develop my own protocol.
Eagerly waiting for reply
Thanks
Yogi
Well, if you're using RS232, you may achieve it by send data to serial com port till reach its end.
For selection and specific queries some protocol may be needed. Also the packet sizes and their repectives addresses can vary . So better if i get a protocol .
MODBus is limited in the packet size. As far as I know, there is no 'standard' for messages that require multiple packets (this is not typically what ModBus) is used for.
In theory, you could adapt some existing packet protocols to meet your needs.
BUT, I am REALLY curious WHY you re attempting to do this?????
[ps: I have done alot of industrial automation, and have NEVER had this type of requirement....]
As posted already in another thread here, a real "protocol" is not actually needed.
All depends of the data type you send. If you send data in a "readable" form like being ASCII characters and numbers to represent names and values, you only have to define an "end-of-transmission" charater like already provided by the ASCII code (hex 04).
If you send binary data and the number of bytes per block is always the same you don't need a protocol either. You simply count out the bytes.
Also a thought could be to make a specified pause of say 500msec after each block to let a timer determine end of transmission of a block.