Re: Modbus configuration issues for the Shimaden SRS10A series digital controllers

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

Hi Feng,

I understand the problem.  For Modbus output drivers, SRS10_Out1 - SRS10_Out7 in your case, the driver attempts an initial read operation from that Modbus address if the pollMsec argument is non-zero.  This allows the EPICS output records to be synchronized to the PLC values when the IOC starts.  This is documented in the pollMsec argument here:

https://epics-modules.github.io/modbus/creating_driver.html#drvmodbusasynconfigure

However, I looked at the manual for your device:

https://www.shimaden.co.jp/dcms_media/other/SRS10A_Manual_Com_en.pdf

Addresses 0x180-x198 are write-only (W/B in the manual).  This means that the read operation will fail, and it generates the Modbus exception 2, "illegal address".  Addresses 0x300 - 0x952 are read/write (R/W/B in the manual).  The is why SRS10_Out6 and SRS10_Out7 do not generate an error message.

You can easily fix the problem.  Just change the pollMsec argument from 1000 to 0 for SRS10_Out1 - SRS10_Out5.

Mark

From: Tech-talk <tech-talk-bounces@aps.anl.gov> on behalf of LONG FENG via Tech-talk <tech-talk@aps.anl.gov>
Sent: Tuesday, December 16, 2025 4:29 AM
To: tech-talk@aps.anl.gov <tech-talk@aps.anl.gov>
Subject: Modbus configuration issues for the Shimaden SRS10A series digital controllers

 

Hi all,

I encountered a strange issue while using the Modbus module to read data from an SRS10A controller. Data reading works correctly, but the problem occurs during data writing.

Part of my st.cmd file is shown below:  

drvAsynIPPortConfigure("SRS", "192.168.1.54:502")

# Enable ASYN_TRACEIO_HEX on octet server
asynSetTraceIOMask(SRS, 0, HEX)

# Enable ASYN_TRACE_ERROR and ASYN_TRACEIO_DRIVER on octet server
asynSetTraceMask(SRS, 0, ERROR|DRIVER)
#modbusInterposeConfig(const char *portName,
#                      modbusLinkType linkType,  # 0=TCP, 1=RTU, 2=ASCII
#                      int timeoutMsec,
#                      int writeDelayMsec)
modbusInterposeConfig("SRS", 0, 1000, 50)
###############################################################
# drvModbusAsynConfigure(
#   char *portName,
#   char *octetPortName,
#   int modbusSlave,
#   int modbusFunction,
#   int modbusStartAddress,
#   int modbusLength,
#   modbusDataType dataType,
#   int pollMsec,
#   char *plcType)

###############################################################

drvModbusAsynConfigure("SRS10_In1", "SRS", 1, 3, 0x100, 8, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_In2", "SRS", 1, 3, 0x109, 3, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_In3", "SRS", 1, 3, 0x10D, 2, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_In4", "SRS", 1, 3, 0x120, 3, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_In5", "SRS", 1, 3, 0x123, 4, 0, 1000,"status")

drvModbusAsynConfigure("SRS10_In6", "SRS", 1, 3, 0x300, 3, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_In7", "SRS", 1, 3, 0x30A, 2, 0, 1000,"status")
#drvModbusAsynConfigure("SRS10_In8", "SRS", 1, 3, 0x400, 18, 0, 1000,"status")
#drvModbusAsynConfigure("SRS10_In9", "SRS", 1, 3, 0x460, 18, 0, 1000,"status")
#drvModbusAsynConfigure("SRS10_In10", "SRS", 1, 3, 0x500, 4, 0, 1000,"status")
#drvModbusAsynConfigure("SRS10_In11", "SRS", 1, 3, 0x508, 4, 0, 1000,"status")
#drvModbusAsynConfigure("SRS10_In12", "SRS", 1, 3, 0x50D, 1, 0, 1000,"status")
#drvModbusAsynConfigure("SRS10_In13", "SRS", 1, 3, 0x510, 4, 0, 1000,"status")
#drvModbusAsynConfigure("SRS10_In14", "SRS", 1, 3, 0x515, 1, 0, 1000,"status")

drvModbusAsynConfigure("SRS10_Out1", "SRS", 1, 6, 0x180, 1, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_Out2", "SRS", 1, 6, 0x182, 4, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_Out3", "SRS", 1, 6, 0x18C, 1, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_Out4", "SRS", 1, 6, 0x190, 3, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_Out5", "SRS", 1, 6, 0x198, 1, 0, 1000,"status")

drvModbusAsynConfigure("SRS10_Out6", "SRS", 1, 6, 0x300, 3, 0, 1000,"status")
drvModbusAsynConfigure("SRS10_Out7", "SRS", 1, 6, 0x30A, 2, 0, 1000,"status")

The following error occurs when I run it：

  2025/12/16 05:15:40.517 drvModbusAsyn::doModbusIO port SRS10_Out1 Modbus exception=2

drvModbusAsynConfigure("SRS10_Out2", "SRS", 1, 6, 0x182, 4, 0, 1000,"status")

2025/12/16 05:15:42.627 drvModbusAsyn::doModbusIO port SRS10_Out2 Modbus exception=2
drvModbusAsynConfigure("SRS10_Out3", "SRS", 1, 6, 0x18C, 1, 0, 1000,"status")

2025/12/16 05:15:43.779 drvModbusAsyn::doModbusIO port SRS10_Out3 Modbus exception=2
drvModbusAsynConfigure("SRS10_Out4", "SRS", 1, 6, 0x190, 3, 0, 1000,"status")

2025/12/16 05:15:44.910 drvModbusAsyn::doModbusIO port SRS10_Out4 Modbus exception=2
drvModbusAsynConfigure("SRS10_Out5", "SRS", 1, 6, 0x198, 1, 0, 1000,"status")

2025/12/16 05:15:46.030 drvModbusAsyn::doModbusIO port SRS10_Out5 Modbus exception=2

Note that SRS10_Out6 and SRS10_Out7 do not produce any errors, and I am indeed able to write data through them normally. This is what confuses me: why do SRS10_Out1 through SRS10_Out5 report errors? I have carefully checked the address settings and did not find any mistakes. Where could the problem be?  

Feng