Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 224)

Detailed Flowcharts
Appendix D
DĆ20
Figure D.25
XMSG Subroutine
XMSG
GETBUF
Check Availabil-
ity
of Receive Buffer
Clear CRC
Accumulator
GETCODE
Get a Code
Link
Data
?
Save
Byte
in Buffer
GETCODE
Get Next Code
Return An
Ignore Flag (0)
Link Data
No
Yes
Return
an ACK
GETBUF
SENDNET
Save New Header
Compare Mes-
sage
with HEADER
A
DLE ETX
?
Message
Too Small
No
Yes
BCC = 0
Re-
turn
a NAK
11678
No
Yes
Yes
Yes
Yes
No
No
No
No
Yes
Yes
No
No
Yes
Yes
Yes
No
No
No
Yes
Output Flag
•
ACK if Message Is OK
•
NAK if Message Is in Error
•
0 if Message Is to be Ignored
Try to Get Another Buffer
Send Link Data to
Network Layer
Duplicate
Message
?
Did Buffer
Overflow
?
Was Buffer
Available
?
Error Flag
?
Buffer
Available
?
Buffer
Overflow
?
Code =
Station No.
?
A