Emacs can communicate with serial ports. For interactive use,
M-x serial-term opens a terminal window. In a Lisp program,
make-serial-process creates a process object.
The serial port can be configured at run-time, without having to
close and re-open it. The function
lets you change the speed, bytesize, and other parameters. In a
terminal window created by
serial-term, you can click on the
mode line for configuration.
A serial connection is represented by a process object, which can be
used in a similar way to a subprocess or network process. You can send and
receive data, and configure the serial port. A serial process object
has no process ID, however, and you can’t send signals to it, and the
status codes are different from other types of processes.
delete-process on the process object or
the process buffer close the connection, but this does not affect the
device connected to the serial port.
process-type returns the symbol
for a process object representing a serial port connection.
Serial ports are available on GNU/Linux, Unix, and MS Windows systems.
Start a terminal-emulator for a serial port in a new buffer. port is the name of the serial port to connect to. For example, this could be /dev/ttyS0 on Unix. On MS Windows, this could be COM1, or \\.\COM10 (double the backslashes in Lisp strings).
speed is the speed of the serial port in bits per second. 9600 is a common value. The buffer is in Term mode; see Term Mode in The GNU Emacs Manual, for the commands to use in that buffer. You can change the speed and the configuration in the mode line menu.
This function creates a process and a buffer. Arguments are specified as keyword/argument pairs. Here’s the list of the meaningful keywords, with the first two (port and speed) being mandatory:
This is the name of the serial port. On Unix and GNU systems, this is a file name such as /dev/ttyS0. On Windows, this could be COM1, or \\.\COM10 for ports higher than COM9 (double the backslashes in Lisp strings).
The speed of the serial port in bits per second. This function calls
serial-process-configure to handle the speed; see the
following documentation of that function for more details.
The name of the process. If name is not given, port will serve as the process name as well.
The buffer to associate with the process. The value can be either a
buffer or a string that names a buffer. Process output goes at the
end of that buffer, unless you specify an output stream or filter
function to handle the output. If buffer is not given, the
process buffer’s name is taken from the value of the
If coding is a symbol, it specifies the coding system used for
both reading and writing for this process. If coding is a cons
(decoding . encoding), decoding is used for
reading, and encoding is used for writing. If not specified,
the default is to determine the coding systems from the data itself.
Initialize the process query flag to query-flag. See Query Before Exit. The flags defaults to
nil if unspecified.
Start process in the “stopped” state if bool is
nil. In the stopped state, a serial process does not
accept incoming data, but you can send outgoing data. The stopped
state is cleared by
continue-process and set by
Install filter as the process filter.
Install sentinel as the process sentinel.
Install plist as the initial plist of the process.
These are handled by
serial-process-configure, which is called
The original argument list, possibly modified by later configuration,
is available via the function
Here is an example:
(make-serial-process :port "/dev/ttyS0" :speed 9600)
This function configures a serial port connection. Arguments are
specified as keyword/argument pairs. Attributes that are not given
are re-initialized from the process’s current configuration (available
via the function
process-contact), or set to reasonable default
values. The following arguments are defined:
Any of these arguments can be given to identify the process that is to be configured. If none of these arguments is given, the current buffer’s process is used.
The speed of the serial port in bits per second, a.k.a. baud
rate. The value can be any number, but most serial ports work only
at a few defined values between 1200 and 115200, with 9600 being the
most common value. If speed is
nil, the function ignores
all other arguments and does not configure the port. This may be
useful for special serial ports such as Bluetooth-to-serial converters,
which can only be configured through ‘AT’ commands sent through the
connection. The value of
nil for speed is valid only for
connections that were already opened by a previous call to
The number of bits per byte, which can be 7 or 8. If bytesize
is not given or
nil, it defaults to 8.
The value can be
nil (don’t use parity), the symbol
odd (use odd parity), or the symbol
even (use even
parity). If parity is not given, it defaults to no parity.
The number of stopbits used to terminate a transmission
of each byte. stopbits can be 1 or 2. If stopbits is not
nil, it defaults to 1.
The type of flow control to use for this connection, which is either
nil (don’t use flow control), the symbol
hw (use RTS/CTS
hardware flow control), or the symbol
sw (use XON/XOFF software
flow control). If flowcontrol is not given, it defaults to no
serial-process-configure for the initial configuration of the