
5–3Data-link Layer Message Frames
Publication
17706.5.16 - October 1996
Full-duplex protocol implements different message frames,
depending on the network layer. This figure shows the format of a
message frame for full-duplex protocol and the layer at which each
portion is implemented:
DST CMD STS
DST CMD STSSRC
DLE STX DLE ETX
BCC/CRC
field
TNS
data
(from application layer)
command data
data from
application layers
From user application program
From common application routines
Datalink layer frame
The
BCC/CRC field contains the 2'
s complement of the 8bit sum (module256 arithmetic sum) of all
application layer data bytes between the DLE STX and the DLE ETX BCC. It does not include any
response symbols. Y
ou can use the BCC/CRC field for one of the following types of error checking:
• block check character (BCC)
• 16bit cyclic redundancy check (CRC16)
Fullduplex Protocol
Message Frames
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