dbx full_duplex_data_link - Manual (Page 4)

Full Duplex Transport Layer Specification Page 4 of 5
the received frame or if the receiving stations receive queue is full, the station should respond with
a NAK flag as NAKs are used for flow control. The sending station should not flag a fault if
NAKs are repeatedly received for the same frame. If no flag is received after a period of at least
250mSec, the transmitting station should perform a resync as described in section 2.5.
Guaranteed/Reliable frame
Frame Start UBYTE 0x64
Frame Count UBYTE 0x01 – 0xFF (not including zero)
VERSION UBYTE 0x01
LEN ULONG Length of entire packet (not including FS FC, CS)
SRC UWORD/ULONG
DEST UWORD/ULONG
MSG_ID UWORD
FLAGS UWORD (there is no guaranteed bit)
(Payload)
Checksum UWORD CCITT-8