6100 BSC Programming Manual

6100 BSC Concepts and Context
If a station is not ready to receive, it can send a NAK or WACK
reply, instead of ACK 0. In that case, the bidder can try again
later or disconnect the line with DLE EOT. Your application
may not send a NAK or a WACK in response to a bid. BSC
sends a NAK for you in the case of certain error conditions;
it does not send a WACK during line bidding, but reports
to you if a WACK is received.
If both stations bid at the same time, it is customary for the
secondary station to yield to the primary. This situation is
described in "Station Types," earlier in this section.
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