Serial/HDLC
| Octet | 0 | 1 | 2 | 3 | |||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Octet | Bit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
| 0 | 0 | HDLC Flag | Ser_Proto (Addr) | Seq_Num (Ctrl) | Dispatch (Protocol) | ||||||||||||||||||||||||||||
| 4 | 32 | o o o | |||||||||||||||||||||||||||||||
| ... | ... | payload | |||||||||||||||||||||||||||||||
| ... | ... | o o o | |||||||||||||||||||||||||||||||
| ... | ... | CRC (lsb) | CRC (msb) | ||||||||||||||||||||||||||||||
| ... | ... | HDLC Flag | |||||||||||||||||||||||||||||||
(Based on T2.1.2 source as of 10/24/2012).
See RFC 1662 for more details.
- HDLC Flag
- (framing) 0x7E, HDLC framing byte. Indicates start of packet.
- Ser_Proto (Addr)
- HDLC Address byte. Used to indicate low level serial protocol. Only 0x44 (68), SERIAL_PROTO_PACKET_ACK and 0x43 SERIAL_PROTO_ACK are supported.
- Seq_Num (Ctrl)
- HDLC Control byte. Used for sequence number. May or may not be present (see NO_TX_SEQNO).
- Dispatch (Protocol)
- HDLC Protocol byte. Used to indicate payload type.
- CRC
- two byte CRC-16, covers all bytes Ser_Proto through last payload byte. This disagrees with TEP 113 (but is from the source code). Transmitted LSB first.
- HDLC flag
- (framing) 0x7E, closing flag
The bytes 0x7D and 0x7E may not appear inside the packet. 0x7E is framing and 0x7D is escape. 0x7D -> 0x7D 0x5d and 0x7E -> 0x7D 0x5E.
