RS-232 Tools

RS-232 is the default mode for all newly opened ports. These five tools provide control over modem signal lines and break conditions — the hardware handshaking and signaling layer of point-to-point serial communication.

get_modem_lines

Read all RS-232 modem control and status line states, including the current break condition.

Parameter	Type	Default	Description
`port`	`str`	required	Device path of the port to query.

Returns: Dict with success, port, input_lines (object with cts, dsr, ri, cd), output_lines (object with rts, dtr), and break_condition (bool).

get_modem_lines(port="/dev/ttyUSB0")

# Example response:
# {
#   "success": true,
#   "port": "/dev/ttyUSB0",
#   "input_lines": {"cts": true, "dsr": true, "ri": false, "cd": false},
#   "output_lines": {"rts": true, "dtr": true},
#   "break_condition": false
# }

set_modem_lines

Set the RS-232 output control lines (RTS and DTR). Only the lines you specify are changed; pass None (or omit the parameter) to leave a line unchanged.

Parameter	Type	Default	Description
`port`	`str`	required	Device path of the port.
`rts`	`bool \| None`	`None`	Set RTS (Request To Send) state. `None` = no change.
`dtr`	`bool \| None`	`None`	Set DTR (Data Terminal Ready) state. `None` = no change.

Returns: Dict with success, port, rts, and dtr (current states after change).

These lines are commonly used for:

Hardware flow control
Device reset sequences (many boards use DTR for reset)
Power control on some devices
Custom signaling protocols

# Assert DTR to signal "terminal ready"
set_modem_lines(port="/dev/ttyUSB0", dtr=true)

# Drop RTS to signal "stop sending"
set_modem_lines(port="/dev/ttyUSB0", rts=false)

# Set both lines at once
set_modem_lines(port="/dev/ttyUSB0", rts=true, dtr=true)

pulse_line

Pulse an RS-232 control line high-then-low or low-then-high. Commonly used for device reset sequences.

Parameter	Type	Default	Description
`port`	`str`	required	Device path of the port.
`line`	`Literal["rts", "dtr"]`	required	Which line to pulse.
`duration_ms`	`int`	`100`	Pulse duration in milliseconds. Must be 1-5000.
`active_low`	`bool`	`True`	If `True`, pulse LOW then HIGH. If `False`, pulse HIGH then LOW.

Returns: Dict with success, port, line, duration_ms, and active_low.

The line is set to its initial state, held for duration_ms, pulsed to the active state for duration_ms, then restored to its original value.

Typical reset sequences:

Arduino: DTR pulse triggers auto-reset
ESP32/ESP8266: DTR + RTS sequence enters bootloader
Custom hardware: Various reset/trigger signals

# Arduino-style reset (DTR pulse, active low)
pulse_line(port="/dev/ttyUSB0", line="dtr", duration_ms=100)

# Active-high pulse on RTS
pulse_line(port="/dev/ttyUSB0", line="rts", duration_ms=200, active_low=false)

# Short trigger pulse
pulse_line(port="/dev/ttyUSB0", line="dtr", duration_ms=10)

send_break

Send a timed serial break signal — a sustained low state on the TX line longer than a character frame. Used to get the attention of a remote device or trigger special modes.

Parameter	Type	Default	Description
`port`	`str`	required	Device path of the port.
`duration_ms`	`int`	`250`	Break duration in milliseconds. Must be 1-5000.

Returns: Dict with success, port, and duration_ms.

# Standard break signal
send_break(port="/dev/ttyUSB0")

# Short break (100ms)
send_break(port="/dev/ttyUSB0", duration_ms=100)

# Long break to force attention
send_break(port="/dev/ttyUSB0", duration_ms=1000)

set_break_condition

Set or clear the break condition on a serial port. Unlike send_break() which sends a timed pulse, this holds the break condition indefinitely until explicitly cleared. Useful for protocols that require sustained break states.

Parameter	Type	Default	Description
`port`	`str`	required	Device path of the port.
`enabled`	`bool`	required	`True` to assert break (hold TX low), `False` to release.

Returns: Dict with success, port, and break_condition.

# Assert break condition
set_break_condition(port="/dev/ttyUSB0", enabled=true)

# ... wait for device to respond ...

# Release break
set_break_condition(port="/dev/ttyUSB0", enabled=false)