When to use direct COM

Most users connect the Seletek via its onboard USB connector, which enumerates as a virtual COM port using the FTDI driver. Direct COM port connection is an alternative that is useful when:

  • You need a hardware COM port with a fixed, guaranteed number that does not change after reboots.
  • You want to use the Seletek with a Raspberry Pi or other single-board computer that has a native UART header.
  • You are integrating the Seletek into a custom enclosure where a separate USB-to-serial adapter with a fixed COM assignment is used.

Connector and pinout

Seletek ARM COM port connector pinout
ARM COM port connector on the Seletek — TXD, RXD, and GND for direct serial connection.

The Seletek's ARM UART runs at 3.3 V logic levels. The connector provides:

  • TXD — serial data from the Seletek to the PC (3.3 V)
  • RXD — serial data from the PC to the Seletek (3.3 V)
  • GND — common ground

Do not connect directly to a PC RS-232 port — RS-232 uses ±12 V signals which will damage the Seletek's UART. Use a 3.3 V USB-to-serial adapter (FTDI, CP2102, CH340, etc.) or a 3.3 V-to-RS-232 level shifter if you need a true RS-232 output.

Software configuration

Seletek software COM port configuration screen
Seletek software connection panel — selecting the direct COM port and baud rate.

In the Seletek software, select the COM port assigned to your serial adapter and set the baud rate to 115200 (the default for the Seletek ARM UART). The software communicates with the Seletek via a simple text-based protocol — no special driver is needed beyond the Windows serial port (or the USB-to-serial adapter's driver).

Flow control: Set hardware flow control to None in the serial port settings. The Seletek UART does not use RTS/CTS flow control.