OpenHAB Modbus bridge with mbusd error

[Brigithubert]

My setup: Got a Komfovent C4 connected (followed IVC wiki) via ch341-uart converter on RPi2B (ttyUSB0) as Modbus gateway.

OpenHAB is running on another RPi in the network.

Polling register 1006 (Modbus address 20) using mbpoll -m rtu -a 20 -b 19200 -t 4 -r 1006 /dev/ttyUSB0 -v on the RPi2B works.

I then setup a configuration for mbusd as follows:

loglevel = 2
logfile = /var/log/mbusd.log
device = /dev/ttyUSB0
speed = 19200
mode = 8e1
trx_control = addc
address = 0.0.0.0
port = 502
maxconn = 32
timeout = 60
retries = 3
pause = 100
wait = 500
replyonbroadcast = no

Installed Modbus bridge on OpenHAB v4.3.5 and created a thing

UID: modbus:tcp:
label: Modbus
thingTypeUID: modbus:tcp
configuration:
rtuEncoded: false
timeBetweenTransactionsMillis: 60
connectMaxTries: 1
reconnectAfterMillis: 100000
port: 502
timeBetweenReconnectMillis: 0
host: 192.168.1.211
connectTimeoutMillis: 10000
afterConnectionDelayMillis: 0
id: 20
enableDiscovery: false

Created another thing "Regular poll"

UID: modbus:poller::
label: Poller
thingTypeUID: modbus:poller
configuration:
start: 1006
length: 1
refresh: 5000
maxTries: 3
cacheMillis: 50
type: input
bridgeUID: modbus:tcp:

This results in (OpenHAB):
COMMUNICATION_ERROR Error with read: org.openhab.core.io.transport.modbus.internal.ModbusSlaveErrorResponseExceptionImpl: Slave responded with error=1 (ILLEGAL_FUNCTION)

Starting mbusd -L /tmp/mbusd.log -p /dev/ttyUSB0 -s 19200 -m 8e1 -P 502 -d -v9 and running the poller in OpenHAB results in

26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 conn_open(): accepting connection from 192.168.1.10
26 Jan 2026 14:15:55 queue_new_elem(): length now is 1
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_HEADER
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 5, t_out = 000000:000060
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_RQST_FUNC
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 5, t_out = 000000:000060
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 conn[192.168.1.10]: read request fc 4
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_RQST_TAIL
26 Jan 2026 14:15:55 conn[192.168.1.10]: request: [14][04][2a][93][00][0a]
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_TTY
26 Jan 2026 14:15:55 tty: state now is TTY_RQST
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 4, t_out = 000000:000060
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 tty: written 8 bytes
26 Jan 2026 14:15:55 tty: request written (total 8 bytes)
26 Jan 2026 14:15:55 tty: state now is TTY_RESP
26 Jan 2026 14:15:55 tty: estimated 25 bytes, waiting 518905 usec
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 tty: read 5 bytes
26 Jan 2026 14:15:55 tty: rx len changed from 25 to 6
26 Jan 2026 14:15:55 tty: read 5 bytes of 6, offset 0
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:55 conn_loop(): select() returns 0
26 Jan 2026 14:15:55 tty: response read (total 5 bytes, offset 0 bytes)
26 Jan 2026 14:15:55 tty: response is correct
26 Jan 2026 14:15:55 tty: response: [14][84][01][93][04]
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_RESP
26 Jan 2026 14:15:55 tty: state now is TTY_PAUSE
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_HEADER
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_RQST_FUNC
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 conn[192.168.1.10]: read request fc 4
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_RQST_TAIL
26 Jan 2026 14:15:55 conn[192.168.1.10]: request: [14][04][2a][93][00][0a]
26 Jan 2026 14:15:55 conn[192.168.1.10]: state now is CONN_TTY
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:55 conn_loop(): select() returns 0
26 Jan 2026 14:15:55 tty: state now is TTY_RQST
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 4, t_out = 000000:000060
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 tty: written 8 bytes
26 Jan 2026 14:15:55 tty: request written (total 8 bytes)
26 Jan 2026 14:15:55 tty: state now is TTY_RESP
26 Jan 2026 14:15:55 tty: estimated 25 bytes, waiting 518905 usec
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:55 conn_loop(): select() returns 1
26 Jan 2026 14:15:55 tty: read 5 bytes
26 Jan 2026 14:15:55 tty: rx len changed from 25 to 6
26 Jan 2026 14:15:55 tty: read 5 bytes of 6, offset 0
26 Jan 2026 14:15:55 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:56 conn_loop(): select() returns 0
26 Jan 2026 14:15:56 tty: response read (total 5 bytes, offset 0 bytes)
26 Jan 2026 14:15:56 tty: response is correct
26 Jan 2026 14:15:56 tty: response: [14][84][01][93][04]
26 Jan 2026 14:15:56 conn[192.168.1.10]: state now is CONN_RESP
26 Jan 2026 14:15:56 tty: state now is TTY_PAUSE
26 Jan 2026 14:15:56 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:56 conn_loop(): select() returns 1
26 Jan 2026 14:15:56 conn[192.168.1.10]: state now is CONN_HEADER
26 Jan 2026 14:15:56 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:56 conn_loop(): select() returns 1
26 Jan 2026 14:15:56 conn[192.168.1.10]: state now is CONN_RQST_FUNC
26 Jan 2026 14:15:56 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:56 conn_loop(): select() returns 1
26 Jan 2026 14:15:56 conn[192.168.1.10]: read request fc 4
26 Jan 2026 14:15:56 conn[192.168.1.10]: state now is CONN_RQST_TAIL
26 Jan 2026 14:15:56 conn[192.168.1.10]: request: [14][04][2a][93][00][0a]
26 Jan 2026 14:15:56 conn[192.168.1.10]: state now is CONN_TTY
26 Jan 2026 14:15:56 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:56 conn_loop(): select() returns 0
26 Jan 2026 14:15:56 tty: state now is TTY_RQST
26 Jan 2026 14:15:56 conn_loop(): select(): max_sd = 4, t_out = 000000:000060
26 Jan 2026 14:15:56 conn_loop(): select() returns 1
26 Jan 2026 14:15:56 tty: written 8 bytes
26 Jan 2026 14:15:56 tty: request written (total 8 bytes)
26 Jan 2026 14:15:56 tty: state now is TTY_RESP
26 Jan 2026 14:15:56 tty: estimated 25 bytes, waiting 518905 usec
26 Jan 2026 14:15:56 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:56 conn_loop(): select() returns 1
26 Jan 2026 14:15:56 tty: read 5 bytes
26 Jan 2026 14:15:56 tty: rx len changed from 25 to 6
26 Jan 2026 14:15:56 tty: read 5 bytes of 6, offset 0
26 Jan 2026 14:15:56 conn_loop(): select(): max_sd = 4, t_out = 000000:000000
26 Jan 2026 14:15:57 conn_loop(): select() returns 0
26 Jan 2026 14:15:57 tty: response read (total 5 bytes, offset 0 bytes)
26 Jan 2026 14:15:57 tty: response is correct
26 Jan 2026 14:15:57 tty: response: [14][84][01][93][04]
26 Jan 2026 14:15:57 conn[192.168.1.10]: state now is CONN_RESP
26 Jan 2026 14:15:57 tty: state now is TTY_PAUSE
26 Jan 2026 14:15:57 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:57 conn_loop(): select() returns 1
26 Jan 2026 14:15:57 conn[192.168.1.10]: state now is CONN_HEADER
26 Jan 2026 14:15:57 conn_loop(): select(): max_sd = 5, t_out = 000000:000000
26 Jan 2026 14:15:57 conn_loop(): select() returns 0
26 Jan 2026 14:15:57 tty: state now is TTY_READY
26 Jan 2026 14:15:57 conn_loop(): select(): max_sd = 5, t_out = 000000:000060

Any idea?

[pflugj]

Try to disable RS-485 support? ( I believe this is for COM-port devices ONLY)

-S Enable RS-485 support for given serial port device (Linux only)

[Brigithubert]

Sry, I updated my post. Needs to be 8e1 instead of 8n1. Now the error message is different.

RS-485 cannot be enabled.

[Brigithubert]

Now it is working... Must have been an issue with OpenHAB.