IEC 60870-5-103 telegram structure
- FT 1.2 frame format is used;
- Frames with fixed and variable block length and single control characters are used;
- Hamming distance = 4;
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 |
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0 | Start byte 1 (0x68) | Header |
| LPCI |
| LPDU | |||||||
1 | Block length |
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2 | Block length (copy) |
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3 | Start byte 2 (0x68) |
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4 | RES | PRM | FCB / ACD | FCV / DFC | Function code | Control field |
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5 | Link address |
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6 | Type identification (monitoring-direction, control-direction) | DATA UNIT IDENTIFIER |
| ASDU |
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7 | SQ | Number of object |
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8 | Cause of transmission (monitoring-direction, control-direction) |
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9 | ASDU address |
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10 |
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11 | Info-object |
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| Information elements |
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n-1 | Checksum | Tail |
| LPCI |
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n | Stop byte (0x16) |
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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 |
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|---|---|---|---|---|---|---|---|---|---|
0 | Start byte 1 (0x10) |
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1 | RES | PRM | FCB / ACD | FCV / DFC | Function code | Control field | |||
2 | Link address |
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3 | Checksum |
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4 | Stop byte (0x16) |
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Single character data
Single characters are used to confirm link layer and user data transmissions.
- 0xE5 (positive acknowledge);