MODBUS_READ_BITS(3)

📦
version 3.1.6 · 3 versions
, in debian bookworm

💖 MODBUS_READ_BITS 💖

okay bestie, so this is modbus_read_bits from libmodbus — it lives in section 3 of the manual (that's the library-functions section, iykyk) and it's literally the glow-up you need when you wanna peek at a whole lil squad of coils at once. ✨

🌸 SYNOPSIS 🌸

int modbus_read_bits(modbus_t *ctx, int addr, int nb, uint8_t *dest);

🦋 DESCRIPTION 🦋

so like, the modbus_read_bits() function shall read the status of the nb bits (coils, bestie — coils!) at the address addr of the remote device. it's giving "hey remote device, spill the tea, what's the vibe on these bits" 💅

the result of reading gets stored in the dest array as unsigned bytes (8 bits each, obviously) set to TRUE or FALSE. no cap.

⚠️ okay now PAY ATTENTION because this part is important: you must take care to allocate enough memory to store the results in dest — at least nb * sizeof(uint8_t). if you don't, that's on you and it will absolutely not be cute. 😭

and fun fact, the function uses the Modbus function code 0x01 (read coil status). iconic behavior fr fr. 👑

✨ RETURN VALUE ✨

on success, the function shall return the number of read bits. slay. 💚

otherwise it shall return -1 and set errno. not the vibe, but at least it tells you why. 🙈

💀 ERRORS 💀

  • EMBMDATA — Too many bits requested. bestie you asked for way too many bits, the request is too big, dial it back. 🫠

🎀 SEE ALSO 🎀

the whole read-and-write bit family, they're a matched set, obsessed honestly. 🫶

👑 AUTHORS 👑

The libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com> — ty for your service, king. 🫡

and that's the whole page, bestie!! this little masterpiece is from libmodbus v3.1.6, dated 11/17/2025, and honestly? main character documentation energy. go read some coils, stay hydrated, allocate your memory properly, mwah 💅💖✨🌸🦋🎀

📦 where this page comes from