IEC 60870-5-102 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 fields

 

 

 

(0, 1 or 2 octets)

 

 

 

Type identification

DATA UNIT IDENTIFIER

 

ASDU

 

 

SQ

Number of object

 

 

 

T

P/N

Cause of transmission

 

 

 

ASDU address fields

 

 

 

(1 or 2 octets)

 

 

 

Record address

 

 

 

Information object address

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

 

 

(0, 1 or 2 octets)

n-1

Checksum

n

Stop byte (0x16)

Single character data

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