lmxopcua/docs/Driver.Modbus.Cli.md

otopcua-modbus-cli — Modbus-TCP test client

Ad-hoc probe / read / write / subscribe tool for talking to Modbus-TCP devices through the same ModbusDriver the OtOpcUa server uses. Mirrors the v1 OPC UA otopcua-cli shape so the muscle memory carries over: drop to a shell, point at a PLC, watch registers move.

First of four driver test-client CLIs (Modbus → AB CIP → AB Legacy → S7 → TwinCAT). Built on the shared ZB.MOM.WW.OtOpcUa.Driver.Cli.Common library so each downstream CLI inherits verbose/log wiring + snapshot formatting without copy-paste.

Build + run

dotnet build src/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli
dotnet run --project src/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli -- --help

Or publish a self-contained binary:

dotnet publish src/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli -c Release -o publish/modbus-cli
publish/modbus-cli/otopcua-modbus-cli.exe --help

Common flags

Every command accepts:

Flag	Default	Purpose
-h / --host	required	Modbus-TCP server hostname or IP
-p / --port	502	TCP port
-U / --unit-id	1	Modbus unit / slave ID
--timeout-ms	2000	Per-PDU timeout
--disable-reconnect	off	Turn off mid-transaction reconnect-and-retry
--verbose	off	Serilog debug output

Commands

probe — is the PLC up?

Connects, reads one holding register, prints driver health. Fastest sanity check after swapping a network cable or deploying a new device.

otopcua-modbus-cli probe -h 192.168.1.10
otopcua-modbus-cli probe -h 192.168.1.10 --probe-address 100    # device locks HR[0]

read — single register / coil / string

Synthesises a one-tag driver config on the fly from --region + --address

• --type flags.

# Holding register as UInt16
otopcua-modbus-cli read -h 192.168.1.10 -r HoldingRegisters -a 100 -t UInt16

# Float32 with word-swap (CDAB) — common on Siemens / some AB families
otopcua-modbus-cli read -h 192.168.1.10 -r HoldingRegisters -a 200 -t Float32 --byte-order WordSwap

# Single bit out of a packed holding register
otopcua-modbus-cli read -h 192.168.1.10 -r HoldingRegisters -a 10 -t BitInRegister --bit-index 3

# 40-char ASCII string — DirectLOGIC packs the first char in the low byte
otopcua-modbus-cli read -h 192.168.1.10 -r HoldingRegisters -a 300 -t String --string-length 40 --string-byte-order LowByteFirst

# Discrete input / coil
otopcua-modbus-cli read -h 192.168.1.10 -r DiscreteInputs -a 5 -t Bool

write — single value

Same flag shape as read plus -v / --value. Values parse per --type using invariant culture (period as decimal separator). Booleans accept true/false/1/0/yes/no/on/off.

otopcua-modbus-cli write -h 192.168.1.10 -r HoldingRegisters -a 100 -t UInt16 -v 42
otopcua-modbus-cli write -h 192.168.1.10 -r HoldingRegisters -a 200 -t Float32 -v 3.14
otopcua-modbus-cli write -h 192.168.1.10 -r Coils -a 5 -t Bool -v on

Writes are non-idempotent by default — a timeout after the device already applied the write will NOT auto-retry. This matches the driver's production contract (plan decisions #44 + #45).

subscribe — watch a register until Ctrl+C

Uses the driver's ISubscribable surface (polling under the hood via PollGroupEngine). Prints every data-change event with a timestamp.

otopcua-modbus-cli subscribe -h 192.168.1.10 -r HoldingRegisters -a 100 -t Int16 -i 500

Output format

• probe / read emit a multi-line per-tag block: Tag / Value / Status / Source Time / Server Time.
• write emits one line: Write <tag>: 0x... (Good | BadCommunicationError | …).
• subscribe emits one line per change: [HH:mm:ss.fff] <tag> = <value> (<status>).

Status codes are rendered as 0xXXXXXXXX (Name) for the OPC UA shortlist (Good, BadCommunicationError, BadTimeout, BadNodeIdUnknown, BadTypeMismatch, Uncertain, …). Unknown codes fall back to bare hex.

Typical workflows

"Is the PLC alive?" → probe.

"Does my recipe write land?" → write + read back against the same address.

"Why is tag X flipping?" → subscribe + wait for the operator scenario.

"What's the right byte order for this family?" → read with --byte-order BigEndian, then with --byte-order WordSwap. The one that gives plausible values is the correct one for that device.