Re: Modbus Module issue

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Luis,

This does look like there is an issue with drvAsynIPPortConfigure on your machine.  The "Unknown error" message seems strange.  You could try the following:

• Change the IP address from 10.136.0.30 to a non-existent IP address on your subnet.  Does the error message change?
• Change port 502 to a port that won't be supported, like 501.  Does the error message change?
• Switch to an IP address and port of another server that should connect, for example port 80 on a Web server.  Does that connect?  I want to see if drvAsynIPPort is working at all.

Just a few minutes ago someone opened this Github issue

https://github.com/epics-modules/asyn/issues/240

It reports a problem with drvAsynIPPortConfigure() on Windows failing with "Unknown error".  This seems suspiciously similar.

Mark

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Luis Alberto De Sousa Moreira via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, July 24, 2026 7:12 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Modbus Module issue

 

Hi Guys,
I think I tried everything I can think off. Still no connection.
May AI assistant thinks that the issue is that the module was built using MinGW instead of the MSVC tool chain, it is talking about the fact that MinGW uses a "Translation Layer" (POSIX vs. Winsock). I never had any issues before so can't see that being the issue, but wondering what you thoughts are on this.

Kind Regards
                 Luis

On 24/07/2026 10:46, Luis Alberto De Sousa Moreira via Tech-talk wrote:

Hi  Jörn,
I think we getting the wires crossed here... the OPCUA port is 4840 but the 502 port is the normal Modbus port. 
I managed to connect fine to it with other applications in the same machine.




Kind Regards
                  Luis

On 24/07/2026 10:38, Jörn Dreyer wrote:

Hi Luis,

are you sure you are using the correct port?
The Beckhoff documentation tells that the OPCUA server is listening on port 4840.  Did you cahnge that when installing the OPCUA Sever on the PLC?
The Ports 500 + x are normally used for the various NC applications in your PLC program.

Regards

Jörn

Am Freitag, 24. Juli 2026, 09:57:38 Mitteleuropäische Sommerzeit schrieb Luis Alberto De Sousa Moreira via Tech-talk:

Just found another application I used before as a Modbus client, called 
EasyModbusClient.
It connects fine and gets data.

This is getting more intriguing...

Best Regards
                   Luis

On 24/07/2026 09:40, Luis Alberto De Sousa Moreira via Tech-talk wrote:

Hi Gabriel,
The firewall seems to be the culprit, but I added rules for the 
application. I also just done a test where I disabled the firewall and 
I get the same result.

D:\FalconDev\EPICS\modbus\iocBoot\iocTest>..\..\bin\windows-x64-mingw\modbusApp.exe 
BPS_Beck.cmd
# BPS_Beck.cmd
# Just testing the modbus module with my BPS Beckhoff PLC.
# 1. Cleanly lock network routing automatically at boot
epicsEnvSet("EPICS_CA_ADDR_LIST", "10.136.0.255")
epicsEnvSet("EPICS_CA_AUTO_ADDR_LIST", "NO")
epicsEnvSet("EPICS_CAS_INTF_ADDR_LIST", "10.136.0.34")
# gvl.mb_Input_Registers[10] := GVL.d_setpoint_T1;              // T1  
                 mS
# gvl.mb_Input_Registers[11] := GVL.d_setpoint_TRamp1;  // Ramp1       
        uS
# gvl.mb_Input_Registers[12] := GVL.d_setpoint_v1;              // V1  
                 10V
# gvl.mb_Input_Registers[13] := GVL.d_setpoint_T2;              // T2  
                 mS
# gvl.mb_Input_Registers[14] := GVL.d_setpoint_TRamp2;  // Ramp2       
        uS
# gvl.mb_Input_Registers[15] := GVL.d_setpoint_V2;              // V2  
                 10V
# gvl.mb_Input_Registers[16] := GVL.d_setpoint_T3;              // T3  
                 mS
# gvl.mb_Input_Registers[17] := GVL.d_setpoint_TRamp3;  // Ramp3       
        uS
# gvl.mb_Input_Registers[18] := GVL.d_setpoint_V3;              // V3  
                 10V
# gvl.mb_Input_Registers[19] := GVL.d_setpoint_pulseLength;     // 
PulseLength  S /mS
# gvl.mb_Input_Registers[20] := GVL.d_setpoint_TRampDown;       // 
RampDown             uS
dbLoadDatabase("../../dbd/modbusApp.dbd")
modbusApp_registerRecordDeviceDriver(pdbbase)
# Get the connection going
drvAsynIPPortConfigure("BPS_Beck", "10.136.0.30:502", 0, 0, 0)
2026/07/24 09:32:59.953 BPS_Beck -1 autoConnect could not connect: 
Can't connect to 10.136.0.30:502: Unknown error
# drvAsynIPPortConfigure("BPS_Beck", "8.8.8.8:8080", 0, 0, 0)
modbusInterposeConfig("BPS_Beck", 0, 5000, 0)
asynSetOption("BPS_Beck",0, "disconnectOnReadTimeout", "Y")
# 
=========================================================================
# Configure Modbus Drivers Memory Blocks
# 
=========================================================================
# Syntax:
# drvModbusAsynConfigure("portName", "tcpPortName", slaveAddress, 
modbusFunction, modbusStartAddress, modbusLength, dataType, pollMsec, 
"plcType")
# drvModbusAsynConfigure("modbusPortName", "asynPortName", 
slaveAddress, modbusFunction, startAddress, length, dataType, 
pollMsec, "plcType")
# Read Coils (Function Code 1)
# Reads 16 binary bits starting at offset 0, polling every 200 
milliseconds.
# drvModbusAsynConfigure("READ_COILS", "PLC_NET", 0, 1, 0, 1, 0, 200, 
"OldPLC")
# Write Coils (Function Code 5)
# Configures a write-only path for coils. pollMsec is 0 because writes 
are instantaneous.
# drvModbusAsynConfigure("WRITE_COILS", "PLC_NET", 0, 5, 0, 1, 0, 0, 
"OldPLC")
# Reads 11 read-only 16-bit registers starting at offset 10, polling 
every 500 milliseconds.
# dataType=0 specifies standard 16-bit unsigned integers (UINT_16).
drvModbusAsynConfigure("READ_INPUTS", "BPS_Beck", 1, 4, 10, 11, 0, 
500, "Beckhoff")
# Read Holding Registers (Function Code 3)
# Reads 1 read/write 16-bit register starting at offset 0, polling 
every 500 milliseconds.
# dataType=0 specifies standard 16-bit unsigned integers (UINT_16).
# drvModbusAsynConfigure("READ_HOLDING", "PLC_NET", 0, 3, 0, 1, 0, 
500, "OldPLC")
# Block E: Write Holding Registers (Function Code 6)
# Configures a write-only path for single registers. pollMsec is 0 for 
on-demand writing.
# drvModbusAsynConfigure("WRITE_HOLDING", "PLC_NET", 0, 6, 0, 1, 0, 0, 
"OldPLC")
# Enable ASYN_TRACEIO_HEX on octet server
# asynSetTraceIOMask("BPS_Beck",0,4)
# Enable ASYN_TRACE_ERROR and ASYN_TRACEIO_DRIVER on octet server
# asynSetTraceMask("BPS_Beck",0,9)
dbLoadRecords("../../db/BPS_Beck.db")
iocInit
Starting iocInit
############################################################################
## EPICS R7.0.10
## Rev. 2026-07-01T08:47+0200
## Rev. Date build date/time:
############################################################################
2026/07/24 09:33:00.992 drvModbusAsyn::doModbusIO port READ_INPUTS 
error calling writeRead, error=asynManager::queueLockPort queueRequest 
failed: port BPS_Beck not connected, nwrite=0/6, nread=0
iocRun: All initialization complete
epics>

Kind Regards
                 Luis



On 23/07/2026 16:24, Gabriel Fedel wrote:

Hi Luis,

Couldn't the firewall be blocking  the EPICS application ?

Best Regards
Gabriel
------------------------------------------------------------------------
*From:* Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Luis 
Alberto De Sousa Moreira via Tech-talk <tech-talk at aps.anl.gov>
*Sent:* Thursday, July 23, 2026 3:59 PM
*To:* Mark Rivers <rivers at cars.uchicago.edu>; tech-talk at aps.anl.gov 
<tech-talk at aps.anl.gov>
*Subject:* Re: Modbus Module issue
Hi Mark,
My other application is using the Modbus protocol, I used it to do the
initial testing on my system.
I tried the telnet command from my MSYS2 environment and it can 
connect...

telnet 10.136.0.30 502
Trying 10.136.0.30...
Connected to 10.136.0.30.
Escape character is '^]'.

Kind Regards
                   Luis

On 23/07/2026 15:31, Mark Rivers wrote:

telnet 10.136.0.30 502

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch