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linuxcnc-modbus/mb2hal.md
bartool 47fc54647d dokumentacja linuxcnc
2026-06-05 17:55:39 +02:00

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1. Introduction

MB2HAL is a generic non-realtime HAL component to communicate with one or more Modbus devices. So far, there are two options to communicate with a Modbus device:

  1. One option is to create a HAL component as a driver see VFD Modbus.
  2. Another option is to use Classic Ladder which has Modbus built in, see ClassicLadder.
  3. Now there is a third option that consists of a "generic" driver configured by text file, this is called MB2HAL.

Why MB2HAL? Consider using MB2HAL if:

  1. You have to write a new driver and you don’t know anything about programming.
  2. You need to use Classic Ladder "only" to manage the Modbus connections.
  3. You have to discover and configure first time the Modbus transactions. MB2HAL have debug levels to facilitate the low level protocol debug.
  4. You have more than one device to connect. MB2HAL is very efficiently managing multiple devices, transactions and links. Currently I am monitoring two axis drivers using a Rs232 port, a VFD driver using another Rs232 port, and a remote I/O using TCP/IP.
  5. You want a protocol to connect your Arduino to HAL. Look the included sample configuration file, sketch and library for Arduino Modbus.

2. Usage

  1. Create a config file from the example below

    • Set component name (optional)

      Set HAL_MODULE_NAME=mymodule (default HAL_MODULE_NAME=mb2hal)

    • Load the modbus HAL non-realtime component

  2. Default component name: loadusr -W mb2hal config=config_file.ini

  3. Custom component name: loadusr -Wn mymodule mb2hal config=config_file.ini

3. Options

3.1 Init Section

[MB2HAL_INIT]

Value Type Required Description
INIT_DEBUG Integer No Debug level of init and INI file parsing
.0 = silent
1 = error messages (default)
2 = OK confirmation messages
3 = debugging messages
4 = maximum debugging messages (only in transactions)
VERSION String No Version number in the format N.N[NN]. Defaults to 1.0.
HAL_MODULE_NAME String No HAL module (component) name. Defaults to "mb2hal".
SLOWDOWN Float No Insert a delay of "FLOAT seconds" between transactions in order to not to have a lot of logging and facilitate the debugging. Useful when using DEBUG=3 (NOT INIT_DEBUG=3). It affects ALL transactions. Use "0.0" for normal activity.
TOTAL_TRANSACTIONS Integer Yes The number of total Modbus transactions. There is no maximum.

3.2 Transaction Sections

One transaction section is required per transaction, starting at [TRANSACTION_00] and counting up sequentially. If there is a new link (not transaction), you must provide the REQUIRED parameters 1st time. Warning: Any OPTIONAL parameter not specified are copied from the previous transaction.

Value Type Required Description
LINK_TYPE String Yes You must specify either a "serial" or "tcp" link for the first transaction. Later transactions will use the previous transaction link if not specified.
TCP_IP IP address If LINK_TYPE=tcp The Modbus slave device IP address. Ignored if LINK_TYPE=serial.
TCP_PORT Integer No The Modbus slave device TCP port. Defaults to 502. Ignored if LINK_TYPE=serial.
SERIAL_PORT String If LINK_TYPE=serial The serial port. For example "/dev/ttyS0". Ignored if LINK_TYPE=tcp.
SERIAL_BAUD Integer If LINK_TYPE=serial The baud rate. Ignored if LINK_TYPE=tcp.
SERIAL_BITS Integer If LINK_TYPE=serial Data bits. One of 5, 6, 7, 8. Ignored if LINK_TYPE=tcp.
SERIAL_PARITY String If LINK_TYPE=serial Data parity. One of: even, odd, none. Ignored if LINK_TYPE=tcp.
SERIAL_STOP Integer If LINK_TYPE=serial Stop bits. One of 1, 2. Ignored if LINK_TYPE=tcp.
SERIAL_DELAY_MS Integer If LINK_TYPE=serial Serial port delay between transactions of this section only. In ms. Defaults to 0. Ignored if LINK_TYPE=tcp.
MB_SLAVE_ID Integer Yes Modbus slave number.
FIRST_ELEMENT Integer Yes The first element address.
NELEMENTS Integer Unless PIN_NAMES is specified The number of elements. It is an error to specify both NELEMENTS and PIN_NAMES. The pin names will be sequential numbers, e.g. mb2hal.plcin.01.
PIN_NAMES List Unless NELEMENTS is specified A list of element names. These names will be used for the pin names, e.g. mb2hal.plcin.cycle_start.
NOTE: There must be no white space characters in the list. Example: PIN_NAMES=cycle_start,stop,feed_hold
MB_TX_CODE String Yes Modbus transaction function code (see specifications):
  • fnct_01_read_coils
  • fnct_02_read_discrete_inputs
  • fnct_03_read_holding_registers
  • fnct_04_read_input_registers
  • fnct_05_write_single_coil
  • fnct_06_write_single_register
  • fnct_15_write_multiple_coils
  • fnct_16_write_multiple_registers
MB_RESPONSE_TIMEOUT_MS Integer No Response timeout for this transaction. In ms. Defaults to 500 ms. This is how much to wait for 1st byte before raise an error.
MB_BYTE_TIMEOUT_MS Integer No Byte timeout for this transaction. In ms. Defaults to 500 ms. This is how much to wait from byte to byte before raise an error.
HAL_TX_NAME String No Instead of giving the transaction number, use a name. Example: mb2hal.00.01 could become mb2hal.plcin.01. The name must not exceed 28 characters. NOTE: when using names be careful that you don’t end up with two transactions using the same name.
MAX_UPDATE_RATE Float No Maximum update rate in Hz. Defaults to 0.0 (0.0 = as soon as available = infinite). NOTE: This is a maximum rate and the actual rate may be lower. If you want to calculate it in ms use (1000 / required_ms). Example: 100 ms = MAX_UPDATE_RATE=10.0, because 1000.0 ms / 100.0 ms = 10.0 Hz.
DEBUG String No Debug level for this transaction only. See INIT_DEBUG parameter above.

3.3. Error codes

While debugging transactions, note the returned "ret[]" value correspond to:

Modbus protocol exceptions:

  • 0x01 - ILLEGAL_FUNCTION - the FUNCTION code received in the query is not allowed or invalid.

  • 0x02 - ILLEGAL_DATA_ADDRESS - the DATA ADDRESS received in the query is not an allowable address for the slave or is invalid.

  • 0x03 - ILLEGAL_DATA_VALUE - a VALUE contained in the data query field is not an allowable value or is invalid.

  • 0x04 - SLAVE_DEVICE_FAILURE - SLAVE (or MASTER) device unrecoverable FAILURE while attempting to perform the requested action.

  • 0x04 - SERVER_FAILURE - (see above).

  • 0x05 - ACKNOWLEDGE - This response is returned to PREVENT A TIMEOUT in the master. A long duration of time is required to process the request in the slave.

  • 0x06 - SLAVE_DEVICE_BUSY - The slave (or server) is BUSY. Retransmit the request later.

  • 0x06 - SERVER_BUSY - (see above).

  • 0x07 - NEGATIVE_ACKNOWLEDGE - Unsuccessful programming request using function code 13 or 14.

  • 0x08 - MEMORY_PARITY_ERROR - SLAVE parity error in MEMORY.

  • 0x0A (-10) - GATEWAY_PROBLEM_PATH - Gateway path(s) not available.

  • 0x0B (-11) - GATEWAY_PROBLEM_TARGET - The target device failed to respond (generated by master, not slave).

Program or connection:

  • 0x0C (-12) - COMM_TIME_OUT

  • 0x0D (-13) - PORT_SOCKET_FAILURE

  • 0x0E (-14) - SELECT_FAILURE

  • 0x0F (-15) - TOO_MANY_DATAS

  • 0x10 (-16) - INVALID_CRC

  • 0x11 (-17) - INVALID_EXCEPTION_CODE

4. Example config file

#This .INI file is also the HELP, MANUAL and HOW-TO file for mb2hal.

#Load the Modbus HAL userspace module as the examples below,
#change to match your own HAL_MODULE_NAME and INI file name
#Using HAL_MODULE_NAME=mb2hal or nothing (default): loadusr -W mb2hal config=config_file.ini
#Using HAL_MODULE_NAME=mymodule: loadusr -Wn mymodule mb2hal config=config_file.ini

# ++++++++++++++++++++++++
# Common section
# ++++++++++++++++++++++++
[MB2HAL_INIT]

#OPTIONAL: Debug level of init and INI file parsing.
# 0 = silent.
# 1 = error messages (default).
# 2 = OK confirmation messages.
# 3 = debugging messages.
# 4 = maximum debugging messages (only in transactions).
INIT_DEBUG=3

#OPTIONAL: Set to 1.1 to enable the new functions:
# - fnct_01_read_coils
# - fnct_05_write_single_coil
# - changed pin names (see https://linuxcnc.org/docs/2.9/html/drivers/mb2hal.html#_pins).
VERSION=1.1

#OPTIONAL: HAL module (component) name. Defaults to "mb2hal".
HAL_MODULE_NAME=mb2hal

#OPTIONAL: Insert a delay of "FLOAT seconds" between transactions in order
#to not to have a lot of logging and facilitate the debugging.
#Useful when using DEBUG=3 (NOT INIT_DEBUG=3)
#It affects ALL transactions.
#Use "0.0" for normal activity.
SLOWDOWN=0.0

#REQUIRED: The number of total Modbus transactions. There is no maximum.
TOTAL_TRANSACTIONS=9

# ++++++++++++++++++++++++
# Transactions
# ++++++++++++++++++++++++
#One transaction section is required per transaction, starting at 00 and counting up sequentially.
#If there is a new link (not transaction), you must provide the REQUIRED parameters 1st time.
#Warning: Any OPTIONAL parameter not specified are copied from the previous transaction.
[TRANSACTION_00]

#REQUIRED: You must specify either a "serial" or "tcp" link for the first transaction.
#Later transaction will use the previous transaction link if not specified.
LINK_TYPE=tcp

#if LINK_TYPE=tcp then REQUIRED (only 1st time): The Modbus slave device ip address.
#if LINK_TYPE=serial then IGNORED
TCP_IP=192.168.2.10

#if LINK_TYPE=tcp then OPTIONAL.
#if LINK_TYPE=serial then IGNORED
#The Modbus slave device tcp port. Defaults to 502.
TCP_PORT=502

#if LINK_TYPE=serial then REQUIRED (only 1st time).
#if LINK_TYPE=tcp then IGNORED
#The serial port.
SERIAL_PORT=/dev/ttyS0

#if LINK_TYPE=serial then REQUIRED (only 1st time).
#if LINK_TYPE=tcp then IGNORED
#The baud rate.
SERIAL_BAUD=115200

#if LINK_TYPE=serial then REQUIRED (only 1st time).
#if LINK_TYPE=tcp then IGNORED
#Data bits. One of 5,6,7,8.
SERIAL_BITS=8

#if LINK_TYPE=serial then REQUIRED (only 1st time).
#if LINK_TYPE=tcp then IGNORED
#Data parity. One of: even, odd, none.
SERIAL_PARITY=none

#if LINK_TYPE=serial then REQUIRED (only 1st time).
#if LINK_TYPE=tcp then IGNORED
#Stop bits. One of 1, 2.
SERIAL_STOP=2

#if LINK_TYPE=serial then OPTIONAL:
#if LINK_TYPE=tcp then IGNORED
#Serial port delay between for this transaction only.
#In ms. Defaults to 0.
SERIAL_DELAY_MS=10

#REQUIRED (only 1st time).
#Modbus slave number.
MB_SLAVE_ID=1

#REQUIRED: The first element address (decimal integer).
FIRST_ELEMENT=0

#REQUIRED unless PIN_NAMES is specified: The number of elements.
#It is an error to specify both NELEMENTS and PIN_NAMES
#The pin names will be sequential numbers e.g mb2hal.plcin.01
#NELEMENTS=4

#REQUIRED unless NELEMENTS is specified: A list of element names.
#these names will be used for the pin names, e.g mb2hal.plcin.cycle_start
#NOTE: there must be no white space characters in the list
PIN_NAMES=cycle_start,stop,feed_hold

#REQUIRED: Modbus transaction function code (see www.modbus.org specifications).
#    fnct_01_read_coils               (01 = 0x01) (new in 1.1)
#    fnct_02_read_discrete_inputs     (02 = 0x02)
#    fnct_03_read_holding_registers   (03 = 0x03)
#    fnct_04_read_input_registers     (04 = 0x04)
#    fnct_05_write_single_coil        (05 = 0x05) (new in 1.1)
#    fnct_06_write_single_register    (06 = 0x06)
#    fnct_15_write_multiple_coils     (15 = 0x0F)
#    fnct_16_write_multiple_registers (16 = 0x10)
#
# Created pins:
# fnct_01_read_coils:
# fnct_02_read_discrete_inputs:
#     mb2hal.m.n.bit     (output)
#     mb2hal.m.n.bit-inv (output)
# fnct_03_read_holding_registers:
# fnct_04_read_input_registers:
#     mb2hal.m.n.float   (output)
#     mb2hal.m.n.int     (output)
# fnct_05_write_single_coil:
#     mb2hal.m.n.bit     (input)
#         NELEMENTS needs to be 1 or PIN_NAMES must contain just one name.
# fnct_06_write_single_register:
#     mb2hal.m.n.float   (input)
#     mb2hal.m.n.int     (input)
#     NELEMENTS needs to be 1 or PIN_NAMES must contain just one name.
#     Both pin values are added and limited to 65535 (UINT16_MAX). Normally use one and let the other open (read as 0).
# fnct_15_write_multiple_coils:
#     mb2hal.m.n.bit     (input)
# fnct_16_write_multiple_registers:
#     mb2hal.m.n.float   (input)
#     mb2hal.m.n.int     (input)
#     Both pin values are added and limited to 65535 (UINT16_MAX). Normally use one and let the other open (read as 0).
#
# m = HAL_TX_NAME or transaction number if not set, n = element number (NELEMENTS) or name from PIN_NAMES
# Example: mb2hal.00.01.<type> (transaction=00, second register=01 (00 is the first one))
#          mb2hal.TxName.01.<type> (HAL_TX_NAME=TxName, second register=01 (00 is the first one))
MB_TX_CODE=fnct_03_read_holding_registers

#OPTIONAL: Response timeout for this transaction. In INTEGER ms. Defaults to 500 ms.
#This is how much to wait for 1st byte before raise an error.
MB_RESPONSE_TIMEOUT_MS=500

#OPTIONAL: Byte timeout for this transaction. In INTEGER ms. Defaults to 500 ms.
#This is how much to wait from byte to byte before raise an error.
MB_BYTE_TIMEOUT_MS=500

#OPTIONAL: Instead of giving the transaction number, use a name.
#Example: mb2hal.00.01 could become mb2hal.plcin.01
#The name must not exceed 28 characters.
#NOTE: when using names be careful that you dont end up with two transactions
#using the same name.
HAL_TX_NAME=remoteIOcfg

#OPTIONAL: Maximum update rate in HZ. Defaults to 0.0 (0.0 = as soon as available = infinite).
#NOTE: This is a maximum rate and the actual rate may be lower.
#If you want to calculate it in ms use (1000 / required_ms).
#Example: 100 ms = MAX_UPDATE_RATE=10.0, because 1000.0 ms / 100.0 ms = 10.0 Hz
MAX_UPDATE_RATE=0.0

#OPTIONAL: Debug level for this transaction only.
#See INIT_DEBUG parameter above.
DEBUG=2

#While DEBUGGING transactions note the returned "ret[]" value correspond to:
#/* Modbus protocol exceptions */
#ILLEGAL_FUNCTION        -0x01 the FUNCTION code received in the query is not allowed or invalid.
#ILLEGAL_DATA_ADDRESS    -0x02 the DATA ADDRESS received in the query is not an allowable address for the slave or is invalid.
#ILLEGAL_DATA_VALUE      -0x03 a VALUE contained in the data query field is not an allowable value or is invalid.
#SLAVE_DEVICE_FAILURE    -0x04 SLAVE (or MASTER) device unrecoverable FAILURE while attempting to perform the requested action.
#SERVER_FAILURE          -0x04 (see above).
#ACKNOWLEDGE             -0x05 This response is returned to PREVENT A TIMEOUT in the master.
#                              A long duration of time is required to process the request in the slave.
#SLAVE_DEVICE_BUSY       -0x06 The slave (or server) is BUSY. Retrasmit the request later.
#SERVER_BUSY             -0x06 (see above).
#NEGATIVE_ACKNOWLEDGE    -0x07 Unsuccessful programming request using function code 13 or 14.
#MEMORY_PARITY_ERROR     -0x08 SLAVE parity error in MEMORY.
#GATEWAY_PROBLEM_PATH    -0x0A (-10) Gateway path(s) not available.
#GATEWAY_PROBLEM_TARGET  -0x0B (-11) The target device failed to repond (generated by master, not slave).
#/* Program or connection */
#COMM_TIME_OUT           -0x0C (-12)
#PORT_SOCKET_FAILURE     -0x0D (-13)
#SELECT_FAILURE          -0x0E (-14)
#TOO_MANY_DATAS          -0x0F (-15)
#INVALID_CRC             -0x10 (-16)
#INVALID_EXCEPTION_CODE  -0x11 (-17)

[TRANSACTION_01]
MB_TX_CODE=fnct_01_read_coils
FIRST_ELEMENT=1024
NELEMENTS=24
HAL_TX_NAME=remoteIOin
MAX_UPDATE_RATE=0.0
DEBUG=1

[TRANSACTION_02]
MB_TX_CODE=fnct_02_read_discrete_inputs
FIRST_ELEMENT=1280
NELEMENTS=8
HAL_TX_NAME=readStatus
MAX_UPDATE_RATE=0.0

[TRANSACTION_03]
MB_TX_CODE=fnct_05_write_single_coil
FIRST_ELEMENT=100
NELEMENTS=1
HAL_TX_NAME=setEnableout
MAX_UPDATE_RATE=0.0

[TRANSACTION_04]
MB_TX_CODE=fnct_15_write_multiple_coils
FIRST_ELEMENT=150
NELEMENTS=10
HAL_TX_NAME=remoteIOout
MAX_UPDATE_RATE=0.0

[TRANSACTION_05]
LINK_TYPE=serial
SERIAL_PORT=/dev/ttyS0
SERIAL_BAUD=115200
SERIAL_BITS=8
SERIAL_PARITY=none
SERIAL_STOP=2
SERIAL_DELAY_MS=50
MB_SLAVE_ID=1
MB_TX_CODE=fnct_03_read_holding_registers
FIRST_ELEMENT=1
NELEMENTS=2
HAL_TX_NAME=XDrive01
MAX_UPDATE_RATE=0.0
DEBUG=1

[TRANSACTION_06]
MB_TX_CODE=fnct_04_read_input_registers
FIRST_ELEMENT=12
NELEMENTS=3
HAL_TX_NAME=XDrive02
MAX_UPDATE_RATE=10.0
DEBUG=1

[TRANSACTION_07]
MB_TX_CODE=fnct_06_write_single_register
FIRST_ELEMENT=20
NELEMENTS=1
HAL_TX_NAME=XDrive03
MAX_UPDATE_RATE=0.0
DEBUG=1

[TRANSACTION_08]
MB_TX_CODE=fnct_16_write_multiple_registers
FIRST_ELEMENT=55
NELEMENTS=8
HAL_TX_NAME=XDrive04
MAX_UPDATE_RATE=10.0
DEBUG=1

5. Pins

Note: sample = New in MB2HAL 1.1 (LinuxCNC 2.9) To use these new features you have to set VERSION = 1.1.

  • m = Value of HAL_TX_NAME if set or transaction number
  • n = Element number (NELEMENTS) or name from PIN_NAMES

Example:

  • mb2hal.00.01.int (TRANSACTION_00, second register)
  • mb2hal.readStatus.01.bit (HAL_TX_NAME=readStatus, first bit)

5.1. fnct_01_read_coils

  • mb2hal.m.n.bit bit out
  • mb2hal.m.n.bit-inv bit out

5.2. fnct_02_read_discrete_inputs

  • mb2hal.m.n.bit bit out
  • mb2hal.m.n.bit-inv bit out

5.3. fnct_03_read_holding_registers

  • mb2hal.m.n.float float out
  • mb2hal.m.n.int s32 out

5.4. fnct_04_read_input_registers

  • mb2hal.m.n.float float out
  • mb2hal.m.n.int s32 out

5.5. fnct_05_write_single_coil

  • mb2hal.m.n.bit bit in

    NELEMENTS needs to be 1 or PIN_NAMES must contain just one name.

5.6. fnct_06_write_single_register

  • mb2hal.m.n.float float in

  • mb2hal.m.n.int s32 in

    NELEMENTS needs to be 1 or PIN_NAMES must contain just one name. Both pin values are added and limited to 65535 (UINT16_MAX). Use one and let the other open (read as 0).

5.7. fnct_15_write_multiple_coils

  • mb2hal.m.n.bit bit in

5.8. fnct_16_write_multiple_registers

  • mb2hal.m.n.float float in

  • mb2hal.m.n.int s32 in

    Both pin values are added and limited to 65535 (UINT16_MAX). Use one and let the other open (read as 0).

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