Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 75)

5–3 Data-link Layer Message Frames
Publication 1770Ć6.5.16 - 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 STS SRC
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
DataĆlink layer frame
The BCC/CRC field contains the 2's complement of the 8Ćbit sum (moduleĆ256 arithmetic sum) of all
application layer data bytes between the DLE STX and the DLE ETX BCC. It does not include any
response symbols. You can use the BCC/CRC field for one of the following types of error checking:
• block check character (BCC)
• 16Ćbit cyclic redundancy check (CRCĆ16)
FullĆduplex Protocol
Message Frames