IEC 60870-5-104 Type IDs Explained: Complete Reference Guide

Every ASDU (Application Service Data Unit) in IEC 60870-5-104 contains a Type ID — a single byte that defines what kind of data the message carries. It tells the receiving station whether the message contains a single-point indication, a measured value, a command, a counter, or a system message.

The Type ID is the first byte of every ASDU. If you misidentify it, you misinterpret the entire message.

IEC 104 shares the same Type IDs as IEC 60870-5-101 (defined in IEC 60870-5-101:2003, Section 7.2.1). This guide covers every Type ID used in IEC 104 — organized by category, with the ASDU name, numeric code, data format, and practical use case for each one.

1. How Type IDs Work

The Type ID is the first field in the ASDU header:

Field	Size	Description
Type ID	1 byte	Identifies the ASDU type (1–127)
Variable Structure Qualifier	1 byte	Number of information objects + SQ bit
Cause of Transmission	1 or 2 bytes	Why this ASDU was sent
Common Address of ASDU	1 or 2 bytes	Station address
Information Object(s)	Variable	The actual data

The Type ID determines:

• What kind of data the ASDU carries (single-point, double-point, measured value, command)
• What information elements are inside each information object (value, quality, timestamp)
• What direction the message travels (monitor = outstation → master, control = master → outstation)

2. Type ID Naming Convention

Every Type ID has a symbolic name following the pattern:

X_YY_ZZ_1

Part	Meaning	Values
X	Direction	M = Monitor (outstation → master), C = Control (master → outstation), P = Parameter, F = File
YY	Data type	SP = Single-Point, DP = Double-Point, ST = Step Position, BO = Bitstring, ME = Measured, IT = Integrated Totals, EP = Event Protection, SC = Single Command, DC = Double Command, SE = Set-point, IC = Interrogation, CI = Counter Interrogation, CS = Clock Sync
ZZ	Qualifier	NA = No time tag, TA = Time tag (3 bytes, CP24Time2a), TB = Time tag CP56Time2a, NC = Short float, ND = Normalized without quality
1	Always 1	Indicates companion standard 101/104

Example: M_ME_TF_1 = Monitor direction, Measured value, short floating point with Time tag CP56Time2a.

3. Process Information in Monitor Direction (Type 1–40)

These ASDUs carry data from the outstation (RTU/IED) to the controlling station (SCADA master).

Single-Point and Double-Point Information

Type ID	Name	Description	Time Tag
1	M_SP_NA_1	Single-point information	None
2	M_SP_TA_1	Single-point information	CP24Time2a (3 bytes)
3	M_DP_NA_1	Double-point information	None
4	M_DP_TA_1	Double-point information	CP24Time2a
30	M_SP_TB_1	Single-point information	CP56Time2a (7 bytes)
31	M_DP_TB_1	Double-point information	CP56Time2a

Single-point = ON/OFF (1 bit). Used for: circuit breaker status, alarm state, digital input.

Double-point = four states: OFF (01), ON (10), Indeterminate (00), Indeterminate (11). Used for: circuit breaker position where intermediate and faulty states must be detected.

Step Position Information

Type ID	Name	Description	Time Tag
5	M_ST_NA_1	Step position information	None
6	M_ST_TA_1	Step position information	CP24Time2a
32	M_ST_TB_1	Step position information	CP56Time2a

Used for: transformer tap changer position (-64 to +63).

Bitstring of 32 Bits

Type ID	Name	Description	Time Tag
7	M_BO_NA_1	Bitstring of 32 bits	None
8	M_BO_TA_1	Bitstring of 32 bits	CP24Time2a
33	M_BO_TB_1	Bitstring of 32 bits	CP56Time2a

Used for: packed status bits, generic binary data where no other type applies.

Measured Values — Normalized

Type ID	Name	Description	Time Tag
9	M_ME_NA_1	Measured value, normalized	None
10	M_ME_TA_1	Measured value, normalized	CP24Time2a
21	M_ME_ND_1	Measured value, normalized without quality	None
34	M_ME_TD_1	Measured value, normalized	CP56Time2a

Normalized values are 16-bit signed integers representing a fraction of a full-scale range (-1.0 to +1.0, encoded as -32768 to +32767). Used for: percentage values, positions.

Measured Values — Scaled

Type ID	Name	Description	Time Tag
11	M_ME_NB_1	Measured value, scaled	None
12	M_ME_TB_1	Measured value, scaled	CP24Time2a
35	M_ME_TE_1	Measured value, scaled	CP56Time2a

Scaled values are 16-bit signed integers with a scaling factor defined by the project. Used for: temperature, pressure, level — when integer representation is sufficient.

Measured Values — Short Floating Point

Type ID	Name	Description	Time Tag
13	M_ME_NC_1	Measured value, short floating point	None
14	M_ME_TC_1	Measured value, short floating point	CP24Time2a
36	M_ME_TF_1	Measured value, short floating point	CP56Time2a

IEEE 754 single-precision float (4 bytes). Used for: voltage, current, power, frequency, energy — the most common measured value type in modern IEC 104 systems.

Integrated Totals (Counters)

Type ID	Name	Description	Time Tag
15	M_IT_NA_1	Integrated totals	None
16	M_IT_TA_1	Integrated totals	CP24Time2a
37	M_IT_TB_1	Integrated totals	CP56Time2a

Used for: energy counters (kWh, kVarh), pulse counters.

Protection Equipment Events

Type ID	Name	Description	Time Tag
17	M_EP_TA_1	Event of protection equipment	CP24Time2a
18	M_EP_TB_1	Packed start events of protection equipment	CP24Time2a
19	M_EP_TC_1	Packed output circuit info of protection equipment	CP24Time2a
38	M_EP_TD_1	Event of protection equipment	CP56Time2a
39	M_EP_TE_1	Packed start events of protection equipment	CP56Time2a
40	M_EP_TF_1	Packed output circuit info of protection equipment	CP56Time2a

Used for: protection relay trip events, fault start detection, output circuit status.

Other Monitor Types

Type ID	Name	Description
20	M_PS_NA_1	Packed single-point information with status change detection

4. Process Information in Control Direction (Type 45–69)

These ASDUs carry commands from the controlling station (SCADA master) to the outstation (RTU/IED).

Commands Without Time Tag

Type ID	Name	Description
45	C_SC_NA_1	Single command (ON/OFF)
46	C_DC_NA_1	Double command (ON/OFF with intermediate states)
47	C_RC_NA_1	Regulating step command (HIGHER/LOWER)
48	C_SE_NA_1	Set-point command, normalized value
49	C_SE_NB_1	Set-point command, scaled value
50	C_SE_NC_1	Set-point command, short floating point
51	C_BO_NA_1	Bitstring of 32 bits command

Commands With CP56Time2a Time Tag

Type ID	Name	Description
58	C_SC_TA_1	Single command with time tag
59	C_DC_TA_1	Double command with time tag
60	C_RC_TA_1	Regulating step command with time tag
61	C_SE_TA_1	Set-point command, normalized with time tag
62	C_SE_TB_1	Set-point command, scaled with time tag
63	C_SE_TC_1	Set-point command, short float with time tag
64	C_BO_TA_1	Bitstring of 32 bits command with time tag

Practical Use

• C_SC_NA_1 (45) — the most common command. Opens/closes a circuit breaker, starts/stops a pump.
• C_DC_NA_1 (46) — used when the target device uses double-point representation (breakers, disconnectors).
• C_RC_NA_1 (47) — raises/lowers a transformer tap changer one step.
• C_SE_NC_1 (50) — sends a floating-point set-point (e.g., voltage set-point to an AVR).

5. System Information in Monitor Direction (Type 70)

Type ID	Name	Description
70	M_EI_NA_1	End of initialization

Sent by the outstation after it completes startup. The SCADA master uses this as a trigger to perform a general interrogation.

6. System Information in Control Direction (Type 100–107)

Type ID	Name	Description
100	C_IC_NA_1	Interrogation command (general interrogation or group)
101	C_CI_NA_1	Counter interrogation command
102	C_RD_NA_1	Read command (read a single information object)
103	C_CS_NA_1	Clock synchronization command
104	C_TS_NA_1	Test command
105	C_RP_NA_1	Reset process command
106	C_CD_NA_1	Delay acquisition command
107	C_TS_TA_1	Test command with CP56Time2a

Practical Use

• C_IC_NA_1 (100) — General Interrogation (GI). The master sends this after startup or reconnection. The outstation responds with all current data.
• C_CI_NA_1 (101) — Counter Interrogation. Requests current counter values.
• C_CS_NA_1 (103) — Clock Synchronization. Aligns the outstation’s clock with the master. Often replaced by NTP/PTP in modern systems.

7. Parameter in Control Direction (Type 110–113)

Type ID	Name	Description
110	P_ME_NA_1	Parameter of measured values, normalized
111	P_ME_NB_1	Parameter of measured values, scaled
112	P_ME_NC_1	Parameter of measured values, short floating point
113	P_AC_NA_1	Parameter activation

Used for: sending deadband and threshold settings to outstations. Less common in modern systems — most parameters are configured via engineering tools.

8. File Transfer (Type 120–127)

Type ID	Name	Description
120	F_FR_NA_1	File ready
121	F_SR_NA_1	Section ready
122	F_SC_NA_1	Call directory, select file, call file, call section
123	F_LS_NA_1	Last section, last segment
124	F_AF_NA_1	ACK file, ACK section
125	F_SG_NA_1	Segment
126	F_DR_TA_1	Directory

Used for: retrieving disturbance records, fault logs, and event files from protection relays and RTUs.

9. The 10 Most Used Type IDs in IEC 104

In a typical power system SCADA installation, these 10 Type IDs account for over 95% of all traffic:

Rank	Type ID	Name	Use
1	36	M_ME_TF_1	Measured values with timestamp (voltage, current, power)
2	30	M_SP_TB_1	Single-point indications with timestamp (breaker status, alarms)
3	31	M_DP_TB_1	Double-point indications with timestamp (breaker position)
4	100	C_IC_NA_1	General Interrogation
5	13	M_ME_NC_1	Measured values without timestamp (cyclic polling)
6	1	M_SP_NA_1	Single-point indications without timestamp (background scan)
7	45	C_SC_NA_1	Single command (open/close breaker)
8	37	M_IT_TB_1	Counter values with timestamp (energy metering)
9	103	C_CS_NA_1	Clock synchronization
10	70	M_EI_NA_1	End of initialization

10. Type IDs with CP56Time2a Timestamps

In IEC 104, the CP56Time2a variant is strongly preferred over CP24Time2a for event reporting. CP56Time2a provides millisecond resolution with full date information (7 bytes).

Without Timestamp	With CP24Time2a	With CP56Time2a	Data Type
1 (M_SP_NA_1)	2 (M_SP_TA_1)	30 (M_SP_TB_1)	Single-point
3 (M_DP_NA_1)	4 (M_DP_TA_1)	31 (M_DP_TB_1)	Double-point
5 (M_ST_NA_1)	6 (M_ST_TA_1)	32 (M_ST_TB_1)	Step position
7 (M_BO_NA_1)	8 (M_BO_TA_1)	33 (M_BO_TB_1)	Bitstring
9 (M_ME_NA_1)	10 (M_ME_TA_1)	34 (M_ME_TD_1)	Measured, normalized
11 (M_ME_NB_1)	12 (M_ME_TB_1)	35 (M_ME_TE_1)	Measured, scaled
13 (M_ME_NC_1)	14 (M_ME_TC_1)	36 (M_ME_TF_1)	Measured, short float
15 (M_IT_NA_1)	16 (M_IT_TA_1)	37 (M_IT_TB_1)	Integrated totals

💡 Best practice: Use CP56Time2a types (30–40) for spontaneous event reporting. Use types without timestamp (1, 3, 9, 11, 13) for cyclic/background scan and general interrogation responses.

11. Quality Descriptors in Monitored Type IDs

Most monitored Type IDs include a quality descriptor byte. The quality bits are:

Bit	Name	Meaning
0	OV	Overflow — measured value exceeded range
4	BL	Blocked — value is frozen/blocked by local operation
5	SB	Substituted — value has been replaced by an operator or system
6	NT	Not Topical — value is not current (e.g., communication lost)
7	IV	Invalid — value is not valid

If bit 7 (IV) = 1, the value should not be trusted. SCADA systems typically show these points with a “bad quality” indicator.

Type 21 (M_ME_ND_1) is the exception — it has no quality descriptor. It is used for fast cyclic transmission where quality is assumed to be good.

12. Cause of Transmission and Type ID Relationships

The Cause of Transmission (COT) in the ASDU header tells the receiving station why the message was sent. Different Type IDs use different COT values:

COT Value	Name	Typical Type IDs
1	Periodic/cyclic	9, 11, 13 (measured values without timestamp)
2	Background scan	1, 3, 9, 11, 13 (all without timestamp)
3	Spontaneous	30, 31, 36 (events with CP56Time2a)
5	Requested (by GI)	1, 3, 9, 11, 13, 30, 31, 36 (GI response)
6	Activation	45, 46, 100 (commands, GI)
7	Activation confirmation	45, 46, 100 (confirmation of command)
10	Activation termination	45, 46, 100 (command execution complete)
20	Interrogated by station	1, 3, 9, 11, 13 (GI group response)
37	Interrogated by group 1	Group-specific interrogation response
44	Unknown Type ID	ASDU rejected by receiving station
45	Unknown COT	ASDU rejected — unknown cause
46	Unknown Common Address	ASDU rejected — wrong station address
47	Unknown IOA	ASDU rejected — unknown information object address

13. Quick Lookup Table: All Type IDs

Monitor Direction (Outstation → Master)

ID	Name	Description
1	M_SP_NA_1	Single-point information
2	M_SP_TA_1	Single-point with time tag CP24
3	M_DP_NA_1	Double-point information
4	M_DP_TA_1	Double-point with time tag CP24
5	M_ST_NA_1	Step position information
6	M_ST_TA_1	Step position with time tag CP24
7	M_BO_NA_1	Bitstring of 32 bits
8	M_BO_TA_1	Bitstring with time tag CP24
9	M_ME_NA_1	Measured value, normalized
10	M_ME_TA_1	Measured normalized with time tag CP24
11	M_ME_NB_1	Measured value, scaled
12	M_ME_TB_1	Measured scaled with time tag CP24
13	M_ME_NC_1	Measured value, short float
14	M_ME_TC_1	Measured short float with time tag CP24
15	M_IT_NA_1	Integrated totals
16	M_IT_TA_1	Integrated totals with time tag CP24
17	M_EP_TA_1	Protection equipment event with time tag CP24
18	M_EP_TB_1	Packed protection start events with time tag CP24
19	M_EP_TC_1	Packed protection output circuit with time tag CP24
20	M_PS_NA_1	Packed single-point with status change detection
21	M_ME_ND_1	Measured normalized without quality
30	M_SP_TB_1	Single-point with time tag CP56
31	M_DP_TB_1	Double-point with time tag CP56
32	M_ST_TB_1	Step position with time tag CP56
33	M_BO_TB_1	Bitstring with time tag CP56
34	M_ME_TD_1	Measured normalized with time tag CP56
35	M_ME_TE_1	Measured scaled with time tag CP56
36	M_ME_TF_1	Measured short float with time tag CP56
37	M_IT_TB_1	Integrated totals with time tag CP56
38	M_EP_TD_1	Protection equipment event with time tag CP56
39	M_EP_TE_1	Packed protection start events with time tag CP56
40	M_EP_TF_1	Packed protection output circuit with time tag CP56

Control Direction (Master → Outstation)

ID	Name	Description
45	C_SC_NA_1	Single command
46	C_DC_NA_1	Double command
47	C_RC_NA_1	Regulating step command
48	C_SE_NA_1	Set-point, normalized
49	C_SE_NB_1	Set-point, scaled
50	C_SE_NC_1	Set-point, short float
51	C_BO_NA_1	Bitstring of 32 bits command
58	C_SC_TA_1	Single command with time tag CP56
59	C_DC_TA_1	Double command with time tag CP56
60	C_RC_TA_1	Regulating step command with time tag CP56
61	C_SE_TA_1	Set-point normalized with time tag CP56
62	C_SE_TB_1	Set-point scaled with time tag CP56
63	C_SE_TC_1	Set-point short float with time tag CP56
64	C_BO_TA_1	Bitstring command with time tag CP56

System Information

ID	Name	Description
70	M_EI_NA_1	End of initialization
100	C_IC_NA_1	Interrogation command
101	C_CI_NA_1	Counter interrogation command
102	C_RD_NA_1	Read command
103	C_CS_NA_1	Clock synchronization command
104	C_TS_NA_1	Test command
105	C_RP_NA_1	Reset process command
106	C_CD_NA_1	Delay acquisition command
107	C_TS_TA_1	Test command with time tag CP56

Parameter

ID	Name	Description
110	P_ME_NA_1	Parameter, normalized
111	P_ME_NB_1	Parameter, scaled
112	P_ME_NC_1	Parameter, short float
113	P_AC_NA_1	Parameter activation

File Transfer

ID	Name	Description
120	F_FR_NA_1	File ready
121	F_SR_NA_1	Section ready
122	F_SC_NA_1	Call directory / select file
123	F_LS_NA_1	Last section, last segment
124	F_AF_NA_1	ACK file, ACK section
125	F_SG_NA_1	Segment
126	F_DR_TA_1	Directory

Summary

The Type ID is the first byte of every IEC 104 ASDU. It defines what kind of data the message carries and how to decode the rest of the frame.

The key things to remember:

• Types 1–40 = monitor direction (outstation → master). Types 30–40 use CP56Time2a timestamps.
• Types 45–64 = control direction (master → outstation). Types 58–64 use CP56Time2a timestamps.
• Type 100 (C_IC_NA_1) = General Interrogation — the most important system command.
• Type 36 (M_ME_TF_1) = the most common measured value type in modern IEC 104 systems.
• Type 30 (M_SP_TB_1) and 31 (M_DP_TB_1) = the most common status indications with timestamps.
• Always check the quality descriptor — bit 7 (IV = Invalid) means the value should not be trusted.
• Use CP56Time2a types (30–40) for spontaneous events. Use types without timestamp for GI responses.

💡 Tip: Use the free IEC 104 Frame Decoder Tool to decode any IEC 104 frame byte by byte — including Type ID, Cause of Transmission, IOA, and data values.

For ASDU structure details, see: IEC 60870-5-104 ASDU Structure

For Wireshark analysis, see: Wireshark IEC 60870-5-104 Decoding Guide