MODBUS_RTU_SET_SERIA(3)

💖 modbus_rtu_set_seria(3) — the libmodbus manual, but make it make sense 💖

okay bestie, pull up a chair, because we're talking about modbus_rtu_set_serial_mode from the libmodbus Manual and honestly? it's giving "small function, big feelings" 🦋

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✨ NAME ✨

modbus_rtu_set_serial_mode — set the serial mode 🎀

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🌸 SYNOPSIS 🌸

int modbus_rtu_set_serial_mode(modbus_t *ctx, int mode);

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💅 DESCRIPTION 💅

so modbus_rtu_set_serial_mode() shall set the selected serial mode, periodt. and your two options are:

• MODBUS_RTU_RS232 — the serial line gets set for RS232 communication. RS-232 (which is short for Recommended Standard 232, no cap) is the traditional name for a whole series of standards for serial binary single-ended data and control signals, connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). it's commonly used in computer serial ports. vintage but iconic, honestly 💜
• MODBUS_RTU_RS485 — the serial line gets set for RS485 communication. EIA-485, also known as TIA/EIA-485 or RS-485, is a standard that defines the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. this standard is widely used for communications in industrial automation because it can be used effectively over long distances and in electrically noisy environments. main character energy in a factory fr fr 🔥

⚠️ okay important one: this function is only supported on Linux kernels 2.6.28 onwards. do not come for me if you're on something older, i warned you 😭

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🌈 RETURN VALUE 🌈

the function shall return 0 if successful 🫶 otherwise it shall return -1 and set errno to one of the values defined below. (yes, the classic. we know her.)

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🎀 ERRORS 🎀

• EINVAL — the current libmodbus backend is not RTU. wrong vibe, wrong mode 🙈
• ENOTSUP — the function is not supported on your platform. not every platform gets to participate, and that's on them 💀

if the call to ioctl() fails, the error code of ioctl will be returned. so like, that error is coming straight from ioctl, not from here. iykyk ✨

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👑 AUTHORS 👑

the libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com> 💖 give credit where credit is due, always.

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that's the whole page bestie, you ate it, you understood it, go set your serial mode 🧚‍♀️

libmodbus v3.1.6 · 11/17/2025 · bye pookie, slay responsibly 💅