========= modbus

Access Modbus devices from the command line

:Author: favalex@gmail.com :Date: 2023-02-26 :Copyright: MPL 2.0 :Version: 0.1.9 :Manual section: 1

SYNOPSIS

modbus [-h] [-r REGISTERS] [-s SLAVE_ID] [-b BAUD] [-p STOP_BITS] [-P {e,o,n}] [-v] device access [access ...]

DESCRIPTION

Read and write registers of Modbus devices.

Access both TCP and RTU (i.e. serial) devices and encode and decode types larger than 16 bits (e.g. floats) into Modbus 16 bits registers.

Optionally access registers by symbolic names, as defined in a registers file. Symbolic names for enumerations and bitfields are supported too.

Designed to work nicely with other standard UNIX tools (watch, socat, etc.), see the examples.

Implemented in python on top of the protocol implementation provided by the umodbus python library.

INSTALL

Regular python install, either pip install modbus_cli to install from pypi or python setup.py install to install from source.

OPTIONS

device /dev/ttyXXX for serial devices, or hostname[:port] for TCP devices

access One or more read or write operations. See ACCESS SYNTAX below.

-r FILE, --registers=FILE Read registers definitions from FILE. Can be specified multiple times. -v, --verbose Print on screen the bytes transferred on the wire. -b BAUD, --baud=BAUD Set the baud rate for serial connections. -p BITS, --stop-bits=BITS Set the number of stop bits for serial connections. -P PARITY, --parity=PARITY Set the parity for serial connections: (e)ven, (o)dd or (n)one -B ORDER, --byte-order=ORDER Set the byte order to one of 'le' (little endian), 'be' (big endian) or 'mixed' -h, --help Show this help message and exit.

ACCESS SYNTAX

[MODBUS_TYPE@]ADDRESS[/BINARY_TYPE][:ENUMERATION_NAME][=VALUE]

Mnemonic: access the register(s) of MODBUS_TYPE starting at ADDRESS, interpreting them as BINARY_TYPE. The / syntax is inspired by gdb (but the available types are different.)

MODBUS_TYPE = h|H|i|c|C|d The modbus type, one of

========== ================ ======= ========= code name size writable ========== ================ ======= ========= h or H holding register 16 bits yes i input register 16 bits no c or C coil 1 bit yes d discrete input 1 bit no ========== ================ ======= =========

Types C and H force the use of "write multiple registers" even when accessing a single register. This is useful for some devices that don't support singular write functions.

The default modbus type is holding register.

ADDRESS = 0-based register address

BINARY_TYPE = Any format description accepted by the python standard pack module. Some common formats are:

===== ==== code type ===== ==== h 16 bits signed integer H 16 bits unsigned integer i 32 bits signed integer I 32 bits unsigned integer f 32 bits IEEE 754 float ===== ====

The default byte order is big-endian. To use little endian, use a < prefix, or --byte-order=le. To use mixed endian (little endian, but individual 16 bit registers are big endian), use --byte-order=mixed.

VALUE = The value to be written to the register. If not present, the register will be read instead.

If only one register is written to, the modbus function 6 (0x6), "write single register" is used. If multiple registers are written to, the modbus function 16 (0x10), "write multiple registers" is used.

EXAMPLES

Read a holding register

$ modbus $IP_OF_MODBUS_DEVICE 100

Write a holding register

$ modbus $IP_OF_MODBUS_DEVICE 100=42

Read multiple registers

To read (or write) multiple registers simply list them on the command line::

$ modbus $IP_OF_MODBUS_DEVICE 100 c@2000

When performing access to multiple contiguous registers, one single modbus operation is performed.

When multiple modbus operations are needed, they are all initiated at once, and the results are collected as they arrive.

More examples of the access syntax

==================== ==== h@39/I read the 32-bits unsigned integer stored in holding registers at addresses 39 and 40 39/I same as above (h is the default modbus type) 39/I=42 write the integer 42 to that register SOME_REGISTER=42 same as above, provided the registers file contains the definition SOME_REGISTER h@39/I 39/I=0xcafe the value can be specified in hexadecimal c@5 read coil at address 5 h@24/f=6.78 write a floating point value to holding registers at addresses 24 and 25 i@1/6B read six unsigned bytes stored in input registers at addresses 1, 2 and 3 ==================== ====

Monitor a register

The UNIX command watch can be used to read a register at regular intervals::

$ watch modbus $IP_OF_MODBUS_DEVICE 100

Read a serial device attached to a remote computer

The UNIX command socat can be used to access a remote device through a TCP tunnel::

remote$ socat -d -d tcp-l:54321,reuseaddr file:/dev/ttyUSB0,raw,b19200 local$ socat -d -d tcp:sc:54321 pty,waitslave,link=/tmp/local_device,unlink-close=0 local$ modbus /tmp/local_device 100

Read multiple registers based on their names

Given the following registers definitions::

$ cat registers.modbus di0 d@0 di1 d@1 ai0 i@512 ai1 i@513

glob matching (*, ?, etc.) can be used to read all the ai registers at once::

$ modbus -r registers.modbus $IP_OF_MODBUS_DEVICE ai*

REGISTERS FILES

The purpose of the registers files is to be able to refer to registers by name.

There can be multiple definition files, specified using either the -r command line switch or the MODBUS_DEFINITIONS environment variable.

A # in a definition file starts a comment.

Each line contains a symbolic name followed by a register definition. The name and the definitions are separated by spaces, for example::

status i@512:STATUS leds 513:LEDS

The file can also contain the possible values for an enumeration or a bitmask, for example::

This is an enumeration named STATUS

:STATUS 0=OFF 1=ON 2=ERROR

This is a bitmask named LEDS

|LEDS 0=LED0 1=LED1 3=LED3 4=LED4

ENVIRONMENT

MODBUS_DEFINITIONS A colon separated list of register definitions files.

favalex / modbus-cli

readme