---
name: "modbus_read_bits"
section: "3"
platform: "linux"
package: "libmodbus-dev"
version: "3.1.6-2.1"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/modbus_read_bits"
---

# modbus\_read\_bits(3)

read many bits

## NAME

modbus\_read\_bits - read many bits

## SYNOPSIS

**int modbus\_read\_bits(modbus\_t \****ctx***, int** *addr***, int** *nb***, uint8\_t \****dest***);**

## DESCRIPTION

The **modbus\_read\_bits()** function shall read the status of the *nb* bits (coils) to the address *addr* of the remote device. The result of reading is stored in *dest* array as unsigned bytes (8 bits) set to TRUE or FALSE.

You must take care to allocate enough memory to store the results in *dest* (at least *nb* \* sizeof(uint8\_t)).

The function uses the Modbus function code 0x01 (read coil status).

## RETURN VALUE

The function shall return the number of read bits if successful. Otherwise it shall return -1 and set errno.

## ERRORS

**EMBMDATA**

Too many bits requested

## SEE ALSO

[**modbus\_write\_bit**(3)](/modbus_write_bit/3.md) [**modbus\_write\_bits**(3)](/modbus_write_bits/3.md)

## AUTHORS

The libmodbus documentation was written by Stéphane Raimbault \<stephane.raimbault@gmail.com\>