Is it possible to request/reply each byte without start, stop bits and parity? In other words the format of each byte in RTU mode may be different from 11 bit.
Hi,
MODBUS is an application layer protocol, whatever physical media you are using is not of concern as far as protocol is concerned. On both ends if you can handle it properly in the physical layer, then it should be possible.
Asynchronous serial communications can't work without start and stop bits - regardless of protocol (MODBUS or other) - it is in the definition of "Asynchronous serial".
Assuming RS232 communications, you need the start and stop bits.
To see why, consider how hex FF is sent. It's 11111111. Each 1 is at the same voltage as line idle, so to send FF I make no change in voltage on the line whatsoever. The receiver cannot determine that I have sent a FF without a start bit and a stop bit to frame the data. There are many examples of ambiguity without start/stop bits.
You could use no parity and go with 10 bits, but I wouldn't. You want your device to interoperate, right?
YES. You can accomplish this by using a synchronous data stream. It is hardware related and the MODBUS protocol should function just the same without any problems.
