grub: serial
16.2.1 serial
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-- Command: serial [--unit=unit] [--port=port] [--speed=speed]
[--word=word] [--parity=parity] [--stop=stop]
Initialize a serial device. UNIT is a number in the range 0-3
specifying which serial port to use; default is 0, which
corresponds to the port often called COM1. PORT is the I/O port
where the UART is to be found; if specified it takes precedence
over UNIT. SPEED is the transmission speed; default is 9600. WORD
and STOP are the number of data bits and stop bits. Data bits must
be in the range 5-8 and stop bits must be 1 or 2. Default is 8
data bits and one stop bit. PARITY is one of 'no', 'odd', 'even'
and defaults to 'no'.
The serial port is not used as a communication channel unless the
'terminal_input' or 'terminal_output' command is used (⇒
terminal_input, ⇒terminal_output).
See also ⇒Serial terminal.