Siemens SIMATIC TIWAY 1 - Manual (Page 200)

USING THE BDLC PROTOCOL
UNILINK HOST ADAPTER B–15
USER MANUAL
The next example, Example B–2, illustrates errors in sequence counts, invalid
commands, and timeouts.
Example B–2 BDLC Error Sequences
Host Computer
(1) I–Frame, N(S)=1, N(R)=0, P
REJ, N(R)=2, F
SNRM
UA
I–Frame, N(S)=0, N(R)=0, P
RR, N(R)=1, F
(2) FRMR
FRMR
(3) I–Frame, N(S)=3, N(R)=2, P
I–Frame, N(S)=3, N(R)=2, P
RR, N(R)=4, F
UNILINK Host
Adapter
... timeout ...
(1) This sequence illustrates an error with the adapter’s receive count. To
clear this condition, the host computer issues a SNRM to reset the
counts and it resets its internal counts, then retransmits the original
I-Frame.
(2) This sequence illustrates an invalid command condition since the
FRMR is not a valid command to the adapter, to which it responds with a
FRMR.
(3) This sequence illustrates a timeout. The host computer did not receive a
response from the adapter before the internal 30 ms time period
expired. The host computer then retransmits the I-Frame, which is
acknowledged by the adapter.