RS-485 Bridge Mode

Mode 3 · Pulsar only · Introduced in firmware v4.4.0

RS-485 Bridge Mode turns the Pulsar into a transparent virtual COM port ↔ RS-485 half-duplex bridge. Bytes written to the port are transmitted on the RS-485 bus through the onboard transceiver, and bus traffic comes back as port input. The firmware switches the transceiver’s direction line automatically, so from the host it looks like an ordinary serial port.

Danger

Not available on Binho Supernova, which has no RS-485 transceiver. Selecting this mode on a Supernova is rejected with an invalid-parameter error.

Tip

Unlike the other exclusive modes, RS-485 runs alongside the normal HID protocol managers. The device keeps servicing I2C, SPI, UART and GPIO commands over HID while bridging RS-485: the two use independent peripherals and pins, so they don’t contend.

Quick start

{% stepper %} {% step %}

Switch the Pulsar into RS-485 mode

python device_settings_cli.py --device pulsar set --cdc-mode rs485

The tool resets the device to apply the change. {% endstep %}

{% step %}

Wire the bus

Connect the transceiver’s A/B differential pair to the RS-485 segment and share a common ground. This is 2-wire half-duplex; the direction line is driven by firmware, so there is nothing to control. {% endstep %}

{% step %}

Open the COM port

Opening the port claims the RS-485 line and configures it. Closing the port releases it and flushes the buffers. {% endstep %} {% endstepper %}

Using the bridge

Set baud rate, data bits, parity and stop bits through the COM port’s normal settings. Changes apply on the fly: there is no need to close the port. Before the host sets anything, the default is 115200 8N1.

Setting	Supported values
Baud rate	Any value the host requests
Data bits	7 or 8
Parity	None, odd, or even
Stop bits	1 or 2

Limitations

• Half-duplex (2-wire) only: there is a single direction line, so 4-wire full-duplex isn’t possible.
• No hardware flow control (RTS/CTS): not applicable to RS-485.
• No 9-bit data, mark/space parity, or 5/6 data bits.
• No multidrop 9th-bit or automatic address matching. The bridge is byte-transparent; addressing belongs to whatever protocol runs over it.
• Transmit blocks until the final stop bit has shifted out, before the driver is released. That guarantees no truncation and no bus contention, but transmit latency grows with payload length and falls with baud rate.

Getting back out

python device_settings_cli.py --device pulsar set --cdc-mode uart_passthrough