Protocol & Address Issues

Most of the time, protocol problems come down to address format, data type, or byte ordering.

Quick Diagnostic

If values are wrong or missing, check these first:

Symptom	Likely Cause	Jump To
All values are 0	Wrong address format	Address Syntax
Huge/tiny numbers (e.g., 1.234e+38)	Byte order mismatch	Byte Ordering
Negative when expecting positive	Signed vs unsigned type	Data Type Mismatch
Random-looking values	Wrong data type size	Data Type Mismatch
"Invalid address" error	Syntax error	Address Syntax
Timeout errors	Connection issue	Gateway Not Connecting

Address Syntax by Protocol

Modbus TCP

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Most Common Mistake

Forgetting to subtract 1 from datasheet addresses. Modbus uses 0-based addressing.

Datasheet Says	Function Code	Proxus Address
`40001`	FC03 (Holding Register)	`x=3;0`
`40100`	FC03 (Holding Register)	`x=3;99`
`30001`	FC04 (Input Register)	`x=4;0`
`30050`	FC04 (Input Register)	`x=4;49`
`00001`	FC01 (Coil)	`x=1;0`
`10001`	FC02 (Discrete Input)	`x=2;0`

Conversion Formula:

Proxus Address = Datasheet Address - Base - 1

40001 series → Base = 40000, x=3
30001 series → Base = 30000, x=4

Example: Device manual says "Speed at register 40201"

Subtract 40000 → 201
Subtract 1 (0-based) → 200
Result: x=3;200

Siemens S7

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Most Common Mistake

Using Word offset instead of Byte offset. Siemens uses byte-based addressing!

TIA Portal Shows	Proxus Address	Data Type
`DB1.DBX0.0`	`DB1.0.0`	Bool
`DB1.DBB10`	`DB1.10`	Byte
`DB1.DBW10`	`DB1.10`	Short/UShort
`DB1.DBD10`	`DB1.10`	Int/Float
`M0.0`	`M0.0`	Bool
`MW100`	`MW100`	Short
`I0.0`	`I0.0`	Bool
`Q0.0`	`Q0.0`	Bool

Common Errors:

Wrong	Correct	Issue
`DB1.DBD0`	`DB1.0`	Remove DBD prefix, just use offset
`DB1.W10`	`DB1.10`	Use byte offset, set type to Short
`DB1.10.8`	`DB1.11.0`	Bits are 0-7, use next byte for bit 8

OPC UA

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Most Common Mistake

Forgetting the namespace index (ns=).

Format	Example
String NodeId	`ns=2;s=Channel1.Device1.Tag1`
Numeric NodeId	`ns=3;i=1001`
Hierarchical	`ns=2;s=PLC/Temperature`

Tip: Use UaExpert to browse and copy the correct Node IDs.

MTConnect

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Most Common Mistake

Using an incomplete Host endpoint (missing scheme/port) or selecting a gateway that cannot reach the machine network.

Item	Format	Example
Host	`http://<ip>:<port>`	`http://192.168.1.20:5000`
Tag Address	`<DeviceName>/<ComponentPath>/<DataItemId>`	`Mazak-01/Controller/exec`
Root-level Tag	`<DeviceName>/<DataItemId>`	`Mazak-01/avail`

Common Errors:

Wrong	Correct	Issue
`192.168.1.20`	`http://192.168.1.20:5000`	Missing explicit endpoint details
`Mazak-01\\Controller\\exec`	`Mazak-01/Controller/exec`	Use `/` separators
`Mazak_01/Controller/exec`	`Mazak-01/Controller/exec`	Device name must match MTConnect device name exactly

Allen-Bradley

Address Type	Format	Example
Tag Name	Direct name	`Program:MainProgram.MyTag`
Array Element	`[index]`	`MyArray[5]`
UDT Member	`.member`	`Motor1.Speed`

Data Type Mismatch

Common Symptoms & Fixes

Symptom	Cause	Solution
Value is half/double expected	Wrong type size (16 vs 32-bit)	Change `Short` ↔ `Int`
Negative when should be positive	Signed vs Unsigned	Use `UShort` instead of `Short`
Decimal missing (10.5 shows as 105)	Integer instead of Float	Change to `Float`
Very large numbers (3.4e+38)	Int read as Float	Change `Float` to `Int`
Value stuck at 65535 or -32768	Overflow from wrong type	Use `Int` instead of `Short`

Type Size Reference

Proxus Type	Size	Value Range
Bool	1 bit	true/false
Byte	8 bit	0 to 255
Short	16 bit	-32,768 to 32,767
UShort	16 bit	0 to 65,535
Int	32 bit	-2.1 billion to 2.1 billion
UInt	32 bit	0 to 4.3 billion
Float	32 bit	±3.4e38 (7 digits precision)
Double	64 bit	±1.7e308 (15 digits precision)

Modbus Register Count

Type	Registers Used
Short/UShort	1 register (16 bit)
Int/UInt/Float	2 registers (32 bit)
Long/Double	4 registers (64 bit)

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Check the Manual

Device manuals usually specify "2 registers" or "32-bit" for values. Match this with your Proxus type.

Byte Ordering Issues

Multi-byte values (Int, Float, Double) can be stored in different byte orders depending on the device manufacturer.

Symptoms of Wrong Byte Order

Float values are extremely large (e.g., 1.234e+38) or tiny (1.4e-45)
Integer values are nonsensical (e.g., 16777216 instead of 1)
Values change wildly with small actual changes

Byte Order Options

Setting	Name	Byte Sequence	Common Devices
`ABCD`	Big Endian	`12 34 56 78`	Most PLCs, Siemens
`DCBA`	Little Endian	`78 56 34 12`	Some sensors
`BADC`	Mid-Big	`34 12 78 56`	Some energy meters
`CDAB`	Mid-Little	`56 78 12 34`	ABB, some VFDs

How to Find the Right Setting

Read a known value (e.g., write 1.0 to a register)
If Proxus shows wrong value, try each byte order setting
Test with distinctive values like 1234.5678 to verify

Setting Byte Order in Proxus

In the Device Profile connection parameters, set the DataFormat field:

Open Data Management > Device Profiles
Select your profile and go to Connection Parameters
Set DataFormat to one of: ABCD, DCBA, BADC, or CDAB

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Modbus TCP

For Modbus TCP devices, the DataFormat parameter is available directly in the connection settings. Other protocol-specific options like isStringReverse may also affect string byte ordering.

Protocol-Specific Errors

Modbus Errors

Error	Meaning	Solution
`Illegal Function (01)`	Function code not supported	Use correct FC (x=1,2,3,4)
`Illegal Data Address (02)`	Register doesn't exist	Check register number in manual
`Illegal Data Value (03)`	Value out of range	Check min/max for register
`Gateway Path Unavailable (0A)`	Wrong Slave ID	Verify Station parameter
`Timeout`	No response	Check IP, port, and network

Siemens S7 Errors

Error	Meaning	Solution
`Connection refused`	PUT/GET disabled	Enable in TIA Portal
`Address not found`	DB doesn't exist	Create DB or check number
`Access denied`	Block protected	Remove protection in TIA
`Invalid slot`	Wrong rack/slot	S7-300/400: Slot 2, S7-1200/1500: Slot 1

OPC UA Errors

Error	Meaning	Solution
`BadSecureChannelClosed`	Server does not trust the client certificate	Trust the Proxus certificate on the OPC UA server (Certificate Trust guide)
`BadSecurityChecksFailed`	Security mode/policy not supported or certificate untrusted	Verify the mode+policy combination matches what the server offers; trust the client certificate
`BadNodeIdUnknown`	Node not found	Verify Node ID with UaExpert
`BadCertificateUntrusted`	Certificate rejected	Add to server's trusted folder
`BadUserAccessDenied`	Wrong credentials	Check username/password
`BadSecurityModeRejected`	Security mismatch	Match security mode with server

MTConnect Errors

Error / Symptom	Meaning	Solution
`No devices found`	Probe returned empty or unreachable endpoint	Verify MTConnect Agent URL and check endpoint from selected gateway network
`Unknown address`	Selected tag path no longer exists in current MTConnect model	Re-open browser and re-select tags from current hierarchy
Frequent `UNAVAILABLE`	Data item currently not published/available	Validate machine state and data item availability in agent output
Browser works on one gateway but not another	Network segmentation / firewall between gateway and machine	Use a gateway in the same machine network zone

Error Code Reference

Below are the actual error codes you may encounter in Proxus logs. These codes indicate specific issues with PLC communication.

Modbus Error Codes

Error Code	Meaning	Solution
`ModbusCRCCheckFailed`	CRC checksum mismatch	Check wiring, baud rate, and parity settings
`ModbusLRCCheckFailed`	LRC checksum mismatch (ASCII mode)	Verify ASCII mode settings match device
`ModbusAsciiFormatCheckFailed`	Invalid ASCII frame format	Ensure device uses Modbus ASCII protocol
`ModbusTcpFunctionCodeNotSupport`	Unsupported function code	Use correct function code (FC01-04)
`ModbusTcpFunctionCodeOverBound`	Register address out of range	Check address exists in device
`ModbusBitIndexOverstep`	Bit index 0-15 exceeded	Use valid bit index within word
`ModbusAddressMustMoreThanOne`	Invalid starting address	Address must be > 0 when offset is enabled

Siemens S7 Error Codes {#s7-errors}

Error Code	Meaning	Solution
`SiemensError000A`	Object does not exist	DB block not found; create in TIA Portal
`SiemensDataLengthCheckFailed`	Block length mismatch	Enable PUT/GET; disable "Optimized block access"
`SiemensReadLengthOverPlcAssign`	Read exceeds PLC limit	Reduce read length or split into multiple reads
`SiemensReadLengthMustBeEvenNumber`	Odd byte length	Data length must be even for word types
`SiemensDBAddressNotAllowedLargerThan255`	DB number > 255	Use DB numbers 1-255 for S7-300/400
`SiemensWriteError`	Write operation failed	Check write permissions and address validity
`SiemensError0006`	Unsupported data type	Use supported types (Bool, Int, Real, etc.)

Mitsubishi/Melsec Error Codes

Error Code	Meaning	Solution
`MelsecError02`	Invalid device range	Check device address exists in PLC
`MelsecErrorC056`	Address exceeded maximum	Reduce address or use extended memory
`MelsecErrorC05F`	Target PLC rejected request	Check network number and PC number
`MelsecErrorC051_54`	Read/write points out of range	Reduce number of points per request
`MelsecErrorC05E`	Communication timeout	Increase timeout or check network
`MelsecFxCrcCheckFailed`	CRC check failed	Verify serial settings (baud, parity)
`MelsecFxReceiveZero`	No response from PLC	Check connection and PLC power
`MelsecCurrentTypeNotSupportedBitOperate`	Bit operation not supported	Use word device for this data type

Omron FINS Error Codes

Error Code	Meaning	Solution
`OmronStatus20`	Connection limit exceeded	Reduce concurrent connections
`OmronStatus21`	Node already connected	Close existing connection first
`OmronStatus22`	Protected network node	Configure node in CX-Programmer
`OmronStatus23`	Network node out of range	Use valid node address (1-126)
`OmronStatus24`	Node already in use	Choose different node address
`OmronStatus25`	All nodes in use	Free up connections on network
`OmronReceiveDataError`	Data receive exception	Check FINS port (9600) and DA1/SA1

Allen-Bradley Error Codes

Error Code	Meaning	Solution
`IOI could not be deciphered`	Tag path invalid	Verify tag name and path syntax
`Tag does not exist`	Tag not found in PLC	Check tag spelling in Studio 5000
`Insufficient memory`	Response buffer overflow	Reduce read size or split requests
`Forward Open failed`	CIP connection rejected	Check slot, IP, and connection limits

Panasonic Mewtocol Error Codes

Error Code	Meaning	Solution
`PanasonicMewStatus40`	BCC error (checksum)	Check serial cable and wiring
`PanasonicMewStatus41`	WACK error - buffer full	Reduce request frequency
`PanasonicMewStatus60`	Parameter error	Check command format and values
`PanasonicMewStatus61`	Data error - BCD overflow	Verify data format (BCD/HEX)
`PanasonicMewStatus63`	PLC mode error	Switch PLC to correct mode
`PanasonicMewStatus65`	Protection error	Disable write protection

Keyence Error Codes

Error Code	Meaning	Solution
`KeyenceNanoE0`	Device/address out of range	Check device number and bank
`KeyenceNanoE1`	Command not supported	Use supported CPU commands
`KeyenceSR2000Error00`	Undefined command	Check command format
`KeyenceSR2000Error20`	Current mode error	Switch to appropriate mode
`KeyenceSR2000Error21`	Buffer full	Wait and retry operation

Yokogawa Link Error Codes

Error Code	Meaning	Solution
`YokogawaLinkError01`	CPU number out of range	Use CPU 1-4
`YokogawaLinkError02`	Command does not exist	Check command spelling
`YokogawaLinkError03`	Device name does not exist	Verify device in program
`YokogawaLinkError42`	Checksum differs	Check cable and connections
`YokogawaLinkError44`	Timeout receiving	Increase timeout; check wiring

Beckhoff ADS Error Codes

Error Code	Meaning	Solution
`ADS Error 1793`	Service not supported	Check TwinCAT version
`ADS Error 1808`	Symbol not found	Verify variable name in PLC
`Target machine not found`	No route to target	Check AmsNetId and route
`Symbol download required`	TPY file outdated	Re-download symbols

Delta DVP Error Codes

Error Code	Meaning	Solution
`Illegal address`	Address not valid	Check device memory map
`Receive check failed`	Checksum error	Verify serial settings
`Response format error`	Invalid response	Check protocol mode

XINJE Error Codes

Error Code	Meaning	Solution
`Address format error`	Invalid address syntax	Use correct format (D100, M0)
`Protocol type error`	Wrong protocol mode	Match protocol to PLC series

GE SRTP Error Codes

Error Code	Meaning	Solution
`Not support bit read/write`	Bit operations blocked	Use word operations
`Address cannot be 0`	Invalid starting address	Start from address 1
`Length must be even`	Odd byte count	Use even byte lengths

Fuji SPB Error Codes

Error Code	Meaning	Solution
`FujiSpbStatus01`	Write to ROM attempted	Check memory area
`FujiSpbStatus02`	Undefined command	Verify command format
`FujiSpbStatus03`	Data contradiction	Check parameter values

LSIS Error Codes

Error Code	Meaning	Solution
`LsisCnet0003`	Blocks exceed 16	Split into smaller requests
`LsisCnet1232`	Max 60 words exceeded	Reduce words per request
`LsisCnet0007`	Invalid data type	Use X, B, W, D, or L types

YASKAWA YRC Robot Error Codes

Error Code	Meaning	Solution
`YRC1010`	Command exception	Check command syntax
`YRC2120`	Data cannot be read	Verify variable access
`YRC3010`	Servo power off	Enable servo power
`YRC5110`	Syntax error	Check command format
`Robot in action`	Robot busy	Wait for motion complete
`Hold is stopping`	In hold state	Release hold signal

Fanuc CNC Error Codes

Error Code	Meaning	Solution
`Protocol error`	Communication failure	Check FOCAS library
`Invalid parameter`	Parameter out of range	Verify parameter values
`CNC not ready`	Machine busy	Wait for ready state

Kuka Robot Error Codes

Error Code	Meaning	Solution
`Variable not found`	KRL variable missing	Create variable in program
`Robot not ready`	Not in correct mode	Switch to EXT/AUTO mode
`Program error`	Submit error	Check KRL syntax

General Connection Errors

Error Code	Meaning	Solution
`ConnectTimeout`	Connection timed out	Check IP, port, and firewall settings
`ReceiveDataTimeout`	No response received	Increase timeout; check device is responding
`ConnectionIsNotAvailable`	Connection dropped	Network issue; will auto-reconnect
`SocketContentReceiveException`	Socket receive error	Check network stability
`IpAddressError`	Invalid IP format	Use format: `192.168.1.100`
`Remote host forcibly closed`	Device disconnected	Check device power and cables

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Finding Error Codes

Filter system logs for protocol-related errors to see protocol-specific context. Original error details are preserved in the log message.

Validation Tools

Use Device Simulators

Before connecting to real hardware, test with simulators:

Modbus: ModRSsim2
OPC UA: Prosys OPC UA Simulation Server
Siemens: PLCSIM Advanced

Use Protocol Analyzers

UaExpert (OPC UA) - Browse, read, write nodes
Modbus Poll - Test Modbus communication
Wireshark - Capture and analyze network traffic

Quick Diagnostic

Address Syntax by Protocol

Modbus TCP

Siemens S7

OPC UA

MTConnect

Allen-Bradley

Data Type Mismatch

Common Symptoms & Fixes

Type Size Reference

Modbus Register Count

Byte Ordering Issues

Symptoms of Wrong Byte Order

Byte Order Options

How to Find the Right Setting

Setting Byte Order in Proxus

Protocol-Specific Errors

Modbus Errors

Siemens S7 Errors

OPC UA Errors

MTConnect Errors

Error Code Reference

Modbus Error Codes

Siemens S7 Error Codes {#s7-errors}

Mitsubishi/Melsec Error Codes

Omron FINS Error Codes

Allen-Bradley Error Codes

Panasonic Mewtocol Error Codes

Keyence Error Codes

Yokogawa Link Error Codes

Beckhoff ADS Error Codes

Delta DVP Error Codes

XINJE Error Codes

GE SRTP Error Codes

Fuji SPB Error Codes

LSIS Error Codes

YASKAWA YRC Robot Error Codes

Fanuc CNC Error Codes

Kuka Robot Error Codes

General Connection Errors

Validation Tools

Use Device Simulators

Use Protocol Analyzers

See Also