(Supplementary node... see 2400bps
300 bytes/sec comes from 2400 bits per second / 8 bits per byte is where this came from.
This number is not entirely correct. Each byte of data transmitted by a serial interface also needs a start bit
and one or more stop bits.
Therefore, each transmitted byte requires at least 10 bits giving a maximum data throughput of 2400 bits per second / 10 bits ber byte of data which equals 240 bytes of data per second.