Instant IEC-104 Decoder – Paste Any IEC-104 Hex Frame, Get Clear Results

The IEC 60870-5-104 protocol (usually called IEC-104) is one of the main communication standards used in SCADA and substation automation. It defines how control centers, RTUs, and gateways exchange data over TCP/IP networks.

If you work with substations, automation, protocol testing, or energy systems, you’ve probably seen IEC-104 hex frames. Reading these frames by hand is slow and error-prone — timestamps, sequence numbers, ASDU types, and object data can get confusing very quickly.

That’s why we built this Free Online IEC-104 Frame Decoder. Just paste your hex frame and the tool instantly explains each field.

What Is an IEC-104 Decoder?

An IEC-104 decoder converts raw hex bytes into a readable structure. Instead of trying to decode control fields and timestamps manually, the tool displays everything clearly, including:

APCI (Application Protocol Control Information)

Frame type (I / S / U)
Send/receive sequence numbers
STARTDT, STOPDT, TESTFR (U-Frames)

ASDU (Application Service Data Unit)

ASDU type (all core + extended types supported)
Variable Structure Qualifier (VSQ)
Cause of Transmission (COT + flags: TEST & NEGATIVE)
ASDU address
Originator address
IOA (Information Object Address)
Object count & sequencing (SQ=0 or SQ=1)

Object-Level Decoding

Depending on ASDU type, the decoder extracts:

Single/double point values
Step positions
Bitstrings (32 bits)
Normalized, scaled, and floating measurements
Integrated totals (counters)
Events with CP24 or CP56 timestamps
Commands (single, double, regulating, setpoints)
Command qualifiers: select/execute + short/long pulse
Quality descriptors
Freeze bits
File transfer types (F_FR, F_SR, F_SC, etc.)
Time sync commands (C_CS, C_TS, C_RD, C_CD…)

The tool supports over 60 ASDU types, including extended timestamped variants.

How the Online IEC-104 Decoder Works

The tool runs 100% inside your browser, which means:

No uploads
No server communication
Completely offline after loading the page

How to use it

Copy any IEC-104 hex frame (from Wireshark, logs, or test tools)
Paste it into the decoder
Press Decode Frame

The output shows:

APCI frame type
Sequence numbers
ASDU type & name
COT meaning
All IOA objects with decoded values
Timestamps (CP24, CP56, CP16)
Quality bits (GOOD/BAD)
Command modes and actions
File service indicators
Raw bytes for unknown types

You can also download the decoded result as a text file.

Why IEC-104 Protocol Is Important

IEC-104 is the TCP/IP version of IEC-101. It uses the same ASDU structure but transmits over Ethernet or any IP network, making it faster and easier to integrate.

You’ll find IEC-104 in:

Electrical substations (telemetry + control)
Energy management systems (EMS/SCADA)
Smart grid devices
Water and gas infrastructure
Industrial automation networks

Because IEC-104 is widely used in critical systems, engineers regularly decode frames to check communication quality, interoperability, and event timing.

Example: Decoding a Real IEC-104 Frame

Input Hex

68 3E 20 00 02 00
22 04 03 00 01 00 E8 03 00 8C 5F 00 18 72 1E 0F
07 0B 19 E9 03 00 E6 42 00 18 72 1E 0F 07 0B 19
EA 03 00 D4 67 00 18 72 1E 0F 07 0B 19 EB 03 00
D7 59 00 18 72 1E 0F 07 0B 19

Decoded Output

All Features Supported by This Decoder

Your decoder supports more than typical online tools, including:

Advanced Timestamp Support

CP24Time2a (3 bytes)
CP56Time2a (7 bytes)
CP16 (delay measurement)

Extended ASDU Types

All measurement variants (normalized/scaled/float)
Timestamped and non-timestamped forms
All counter types (IT, EP, PS)
Event types (M_SP_TB_1, M_ME_TD, etc.)
File services (F_FR, F_SR, F_SC, F_LS, F_AF, F_SG, F_DR…)

Full Command Decoding

Single commands (C_SC)
Double commands (C_DC)
Regulating commands (C_RC)
Setpoints (C_SE) normalized / scaled / float
Time-tagged setpoints
Select/Execute logic
Pulse modes: short, long, persistent

COT (Cause of Transmission)

All causes 1–41 + group interrogations (21–36), counters, commands, initialization.

APCI

I-Frames
S-Frames
U-Frames (STARTDT, STOPDT, TESTFR)

Error Handling

Invalid length
Truncated IOA
Unsupported types → raw byte fallback

This is one of the most complete free IEC-104 decoders available.

Who Uses This IEC-104 Decoder

This tool is useful for:

SCADA & Substation engineers
Test automation engineers
RTU/IED developers
Protocol integration teams
Cybersecurity analysts
Students & researchers learning IEC-104

If you deal with energy automation, communication debugging, or protocol testing, this decoder saves hours of manual work.

FAQ

Is the decoder accurate for all ASDU types?

It supports all major IEC-104 types (1–112+) including extended timestamp formats. Unsupported types automatically show raw bytes.

Does it work offline?

Yes. Once the page loads, everything runs locally in JavaScript.

How is this different from Wireshark?

Wireshark is designed to analyze full network packet captures, while this tool is built to be fast, lightweight, and focused solely on IEC-104 frame decoding, making it much easier to use for training, debugging, and documentation.

Conclusion

The Online IEC-104 Decoder is the easiest way to decode IEC-104 frames in your browser. No installation. No uploads. No complicated filters.

Just paste a frame, click decode, and instantly see:

APCI
ASDU
COT
IOA
Values
Quality
CP24/CP56 timestamps
Commands
File services
Everything else inside the frame

Try it now — paste your IEC-104 hex frame and decode it instantly.

Decode Your IEC-104 Frame Online

Give it a try: just paste your IEC-104 hex frame and hit Decode Frame to view the results instantly.

Support & Feedback

If you run into problems or see unexpected output, we’re here to help.

When contacting support, include:

Decoder name (IEC-104 Decoder, IEC-101 Decoder, Modbus, DNP3, etc.)
Description of issue
Hex frame you tested
Any error messages displayed

This helps us diagnose and improve the tool faster.

Contact Support: SCADA Protocols Support Page