Detailed Description

Modbus Plus HDLC token-bus frame codec (DETWS_ENABLE_MBPLUS).

Modbus Plus is Schneider's 1 Mbit/s token-passing peer bus. Its data link is HDLC-framed: a frame is delimited by the HDLC flag 0x7E, carries an address / control / the LLC+Modbus routing path + data, and ends with a CRC-16 (CRC-16/X-25). This codec builds/validates the HDLC frame (with 0x7E-flag delimiting and the standard bit/byte transparency handled at the byte level) around a Modbus routing path + PDU, plus the token-rotation helper that computes the next station in the logical ring:

[7E][address][control][routing path...][data...][CRC-16 lo][CRC-16 hi][7E]

The physical 1 Mbit/s bus is hardware-gated; this is the frame + token-MAC layer, reusing the shipped Modbus PDU model for the data. Pure, zero heap, no stdlib, host-testable.

Definition in file mbplus.h.