IEC 60870-5-103 telegram structure

Frame with variable length

This frame type is used to transmit user data between controlling and controlled station

byte\bit

7

6

5

4

3

2

1

0

0

Start byte 1 (0x68)

Header

LPCI

LPDU

1

Block length

2

Block length (copy)

3

Start byte 2 (0x68)

4

RES

PRM

FCB / ACD

FCV / DFC

Function code

Control field

5

Link address

6

Type identification (monitoring-direction, control-direction)

DATA UNIT IDENTIFIER

ASDU

7

SQ

Number of object

8

Cause of transmission (monitoring-direction, control-direction)

9

ASDU address

10

Function type

11

Information number

Info-object

Information elements

n-1

Checksum

Tail

LPCI

n

Stop byte (0x16)

Frame with fixed length

This frame type is used for link layer services. Sometimes used as an confirmation.

byte\bit

7

6

5

4

3

2

1

0

0

Start byte 1 (0x10)

1

RES

PRM

FCB / ACD

FCV / DFC

Function code

Control field

2

Link address

3

Checksum

4

Stop byte (0x16)

Single character data

Single characters are used to confirm link layer and user data transmissions.