Re: Modbus problem bit swap Wago PLC

["Brown, Garth via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Jeffery,

Do you use the same modbusFunction with both types in your drvModbusAsynConfigure command? A few years ago I was working with a Pilz PLC, and it surprised me to find that the bit order, but not the byte order, changed depending on which modbusFunction I specified.

-Garth Brown

SLAC National Accelerator Laboratory

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, May 2, 2025 12:28 PM
To: Jeffrey Gamsby <jfgamsby at lbl.gov>; tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: RE: Modbus problem bit swap Wago PLC

 

Hi Jeffrey,

 

What do you mean by “bit-swap”?  Do you mean the values 0 and 1 are swapped, or that the order of the bits is swapped?

 

Mark

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Jeffrey Gamsby via Tech-talk
Sent: Friday, May 2, 2025 5:29 AM
To: tech-talk at aps.anl.gov
Subject: Modbus problem bit swap Wago PLC

 

Hi All,

 

 I am using a Wago PLC and Epics asyn-R4-43/Modbus R3-2, and I am seeing some differences in the FC2 reads depending on the Wago module that is used.   

 

If the 750-400/500 series module DO/DI are used, the reads come back as expected, but if the 750-1400/1500 series are used there is a bit swap when reading.

 

Here is my current Asyn port configuration, I have tried the different data types as enums and strings but that doesn't change anything.

 

I can make it work, just trying to understand why I get the bit swap when using different modules on the PLC. 

 

Here is my config:

 

cmd file:

# Bit read access, Function code 2
drvModbusAsynConfigure("FC2", "sim1", 0, 2,  0, 32, 0, 100, "Wago")

 

and the db record

# bi record template for register inputs
record(bi,"$(P)$(R)") {
    field(DTYP,"asynUInt32Digital")
    field(INP,"@asynMask($(PORT) $(OFFSET) 0x1)")
    field(SCAN,"$(SCAN)")
    field(ZNAM,"$(ZNAM)")
    field(ONAM,"$(ONAM)")
    field(ZSV,"$(ZSV)")
    field(OSV,"$(OSV)")
}

 

 

and my substitutions file:

 

# READ COILS - FUNCTION CODE 2
# Reads WAGO MB Output Bits
file "$(MODBUS)/db/bi_bit.jeff.template" { pattern
{P,        R,        PORT,    OFFSET,      ZNAM,   ONAM,  ZSV,       OSV,    SCAN}
{SIM1:,    FC2_0,     FC2,     0,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_1,     FC2,     1,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_2,     FC2,     2,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_3,     FC2,     3,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_4,     FC2,     4,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_5,     FC2,     5,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_6,     FC2,     6,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_7,     FC2,     7,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_8,     FC2,     8,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_9      FC2,     9,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_10,     FC2,     10,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_11,     FC2,     11,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_12,     FC2,     12,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_13,     FC2,     13,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_14,     FC2,     14,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
{SIM1:,    FC2_15,     FC2,     15,        Low,    High,  NO_ALARM,  MAJOR,  "1 second"}
}