IEC101Scop Slave is a free IEC 60870-5-101 controlled-station simulator with a modern, dockable Dear ImGui interface — part of the Scop family alongside ModbusScop, DNPScop, and IEC104Scop, sharing their look and feel. It emulates one or many IEC 101 stations on a serial line (FT1.2) or behind a TCP tunnel (terminal servers and serial-to-Ethernet gateways), in unbalanced or balanced link mode, so engineers can test, commission, and troubleshoot IEC 101 masters and SCADA front ends without real field hardware.
The complete IEC 101 stack — the FT1.2 link layer with its secondary-station procedures and the ASDU / information-object codec shared with IEC104Scop — is hand-rolled over Asio, with no third-party protocol library.
Free to use and redistribute under the permissive BSD 2-Clause License.
Developed by Carlos Nardi.
IEC101Scop Slave is organized as a tree: Channels → RTUs → Points.
- A Channel is one secondary-station link: a Serial COM port (baud, parity, stop bits) or a TCP (FT1.2 tunnel) listener on a bind address and port. Each channel sets its link address, the link mode (unbalanced / polled, or balanced / point-to-point with ACK timeout and retries), and the -101 field sizes (link address, cause of transmission, common address, and information-object address). Each channel runs on its own I/O thread; start and stop them independently.
- An RTU is one simulated station with its own common address (CA) inside a channel. A channel can host many RTUs and routes every ASDU to the matching common address. Each RTU has its own cyclic, background-scan, and double-transmission settings.
- Each RTU carries a point database — Indications (single-point, double-point, step position), Measurands (normalized, scaled, float), Counters (integrated totals), and Controls (single, double, and regulating-step commands, setpoints) — editable directly in the UI, each point with its own quality, time tag, event type, simulation, and control permission.
- Complete hand-rolled IEC 101 stack over Asio (no third-party library): FT1.2 single-character, fixed-length, and variable-length frames with checksum and resynchronization; secondary-station procedures for Reset Link and Request Status, FCB duplicate detection with repeat of the last response, ACD signalling of pending Class 1 data, separate Class 1 (events, command and interrogation replies) and Class 2 (cyclic and background) buffers, and balanced-mode SEND / CONFIRM transmission with ACK timeout and retries.
- Serial and TCP tunnel — serve a master on a real COM port or accept an FT1.2-over-TCP connection, chosen per channel.
- Configurable -101 profile — link address size (0 / 1 / 2 octets), cause of transmission (1 octet or 2 with originator), common address (1 / 2 octets), and IOA (1 / 2 / 3 octets) per channel, matching the master's engineering.
- Multi-station simulation — many channels, each with many stations on distinct common addresses.
- Full point model — M_SP, M_DP, M_ST, M_ME_NA/NB/NC (normalized / scaled / float), and M_IT, each selectable per point as plain, CP24Time2a, or CP56Time2a time-tagged; the measurand type is switchable in place.
- Interrogation, counters, and clock — answers General Interrogation (C_IC) and Counter Interrogation (C_CI) with the station image and accepts Clock Synchronization (C_CS), tracking the master's time offset.
- Spontaneous, cyclic, and background transmission — per-point spontaneous events (COT 3) on change, per-RTU cyclic transmission (COT 1) of flagged measurands, a periodic background scan (COT 2) of the whole database, and optional double transmission (plain type followed by the time-tagged twin).
- Commands + glue logic — executes Single (C_SC), Double (C_DC), Regulating Step (C_RC) and normalized / scaled / float Setpoints (C_SE_NA/NB/NC) with select / execute. A per-point Linked IOA mirrors the command onto a monitor point, and the Glue Logic editor maps command triggers (any / ON / OFF / LOWER / RAISE, by qualifier) to actions — Set to Value, Pulse, Increment, Decrement, Randomize, Set to Command Value — on any point.
- Fault injection — per-point control permission (Allow, Deny selection, Deny execution, No control — refusals mirror the command with the NEGATIVE bit) and per-point quality flags (IV, NT, SB, BL, OV).
- Per-point simulation — Sine, Ramp, Random, Increment, and Toggle, constrained by each point's type and paced per point, with a global Start Sim / Stop Sim button and a 0.1× – 10× speed slider.
- Editable point windows — a Master-style grid per RTU with sorting, multi- select editing that propagates to every selected point, engineering scaling (Eng Min / Eng Max / units), and CSV export / import of the complete point definition (values, quality, time tag, simulation, permissions, links).
- Animation — rows flash when a master commands them, when simulation or spontaneous events change them, or when you edit them by hand — three configurable colors under Setup → Animation; the tree blinks on traffic.
- Communication Monitor — a timestamped, filterable log of every frame per channel, master, and RTU, with a layered link / ASDU decode of the selected frame using the channel's field sizes, and optional log-to-file with size-based rotation.
- Status Messages & Dashboard — master connect/disconnect, command execution and refusal traces, clock-sync events, plus live per-channel Tx / Rx counters and uptime.
- Workspaces — save and reload your entire setup (
.i1sw): channels (transport, serial parameters, link address and mode, field sizes, balanced ACK timing, running state), stations, points with values, quality, event types, simulations, permissions, links, and glue rules. Channels that were running are started again on load. - Themes — dark / light / classic with a customizable accent color, DPI scaling, and always-on-top; layout and preferences are remembered between runs.
- Go to the Releases page and download the latest
IEC101ScopSlavearchive for Windows. - Unzip it anywhere and run
IEC101ScopSlave.exe— no installation required.
Requirements: Windows 10/11 (64-bit).
Rendering: IEC101Scop Slave uses the GPU by default; you can switch to CPU (software) rendering under View → Rendering (handy over Remote Desktop or in VMs).
- + Channel — choose Serial COM (port, baud, parity, stop bits) or TCP
(FT1.2 tunnel) (bind address, port), then set the link address, the
link mode, and — if the master expects something other than the defaults —
the -101 field sizes. The channel is created with one RTU (common address
- and starts immediately.
- Add RTU... — add more stations, each with its own common address; open Settings... on an RTU for cyclic, background-scan, and double-transmission periods.
- Open the RTU's Points window, add information objects by type and IOA, then edit values, quality, time tags, simulations, permissions, and glue logic directly in the grid. Press Start Sim to animate the simulated points.
- Point your IEC 101 master at the COM port (or the TCP tunnel's IP and port). Watch the frames decode in the Communication Monitor and the counters in the Dashboard.
Use File → Save Workspace (Ctrl+S) to keep the whole configuration and reload it later with Open Workspace (Ctrl+O).
IEC101Scop Slave is built with these open-source components, each under its own license:
| Library | Used for | License |
|---|---|---|
| Dear ImGui (docking) | user interface | MIT |
| GLFW 3 | window / OpenGL context | Zlib/libpng |
| OpenGL 3 | rendering | — |
| Asio (standalone) | serial / TCP transport | Boost Software License 1.0 |
| stb_image | logo / splash decoding | MIT / public domain |
The IEC 60870-5-101 protocol stack itself (FT1.2 link layer, ASDU codec, station database, controlled-station engine) is original code, not a third-party library.
IEC101Scop Slave is released under the BSD 2-Clause License. It is provided "as is", without warranty of any kind; the author is not responsible for any damage or loss caused by its use.
BSD 2-Clause License
Copyright (c) 2026, Carlos Nardi
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