The start bit is always sent, and therefore is not a factor you have to consider when creating devices for Neets control systems. The start bit is always only 1 bit long, so therefore not a variable you can change, it’s a part of the RS-232 standard.
The stop bit is the last bit that is sent when sending a byte. The purpose of the stop bit is to inform the receiver that the transmission of this byte is complete. The stop bit and the start bit are always sent.
This means that even if you try to send “nothing,” something will always be sent. Like the speed, both the transmitter and receiver must be set to use the same number of stop bits (1, 1.5, or 2) for each byte.