Siemens SIMATIC TIWAY 1 Manual De Usuario
USING THE BDLC PROTOCOL
UNILINK HOST ADAPTER
B–11
USER MANUAL
B.5.4
BCS Error
When the Block Checksum calculated by the receiver does not match the BCS in
the I-Frame, the receiving station completely ignores the message. This is
because with an incorrect checksum, there is no guarantee that the address
field contains the correct address. Recovery is then initiated by the sending
station when the timeout period expires.
the I-Frame, the receiving station completely ignores the message. This is
because with an incorrect checksum, there is no guarantee that the address
field contains the correct address. Recovery is then initiated by the sending
station when the timeout period expires.
B.5.5
Timeout Errors
The adapter should always respond to a host computer BDLC command within
30 ms. If it does not, the host computer should try to retransmit the
unacknowledged I-Frames. Timeouts are caused by receiving a frame with a
BCS error, in which case the adapter does nothing, and by the adapter going
offline (no power or host port media is disconnected).
30 ms. If it does not, the host computer should try to retransmit the
unacknowledged I-Frames. Timeouts are caused by receiving a frame with a
BCS error, in which case the adapter does nothing, and by the adapter going
offline (no power or host port media is disconnected).
B.5.6
RR and REJ Recovery
When the sending station receives an RR or REJ with an N(R) sequence count
less than its internal send count, it should retransmit the unacknowledged
I-Frames.
less than its internal send count, it should retransmit the unacknowledged
I-Frames.