Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 47)

Asynchronous Link Protocols
Chapter 4
4-4
Figure 4.1
Packet Format for Full-Duplex Protocol
CMD STS Command/Response Block
DST SRC CMD STS TNS
Data
(From Application Layer)
DLE STX Data
(From Network Layer)
DLE ETX
From
Application
Layer
From
Network
Layer
11321A
BCC Data Link
Layer Packet
Block Check
The block check character (BCC) is a means of checking the accuracy of
each message packet transmission. It is the 2’s complement of the 8-bit
sum (modulo-256 arithmetic sum) of all data bytes between the DLE STX
and the DLE ETX BCC. It does not include any other message packet
codes or response codes.
Example 1: If a message packet contained the data codes 08, 09, 06, 00,
02, 04 and 03, the message packet codes would be (in hex):
10
DLE STX
02 08 09 06 00 02 04 03 10 03 E0
DLE ETX BCC Data