6100 BSC Programming Manual

6100 BSC Concepts and Context
An arriving NAK completes the request that sent the TTD. The
application can repeat the TTD as often as the other station
allows, i.e., as often as its retry count permits. Then it
must either send its next block or relinquish the line.
Forward Abort. If after a TTD sequence a station sends an EOT as
its next transmission, the EOT means "I can't send more data.
I'm too busy, or an error has occurred." Without the preceding
TTD, the EOT would be a normal end of transmission. Figure 1-12
illustrates this contrast: the first EOT ends transmission
normally; the second is an abnormal end of transmission. In
either case, the receiving station may bid for the line; a
station that cannot transmit may still be able to receive. The
application makes a READ request to send the EOT sequence; it
does not supply the sequence in its output buffer.
NOTE
The contrast shown in Figure 1-12 is transparent to the
receiving application. However, if the contrast is
important to the remote station, BSC provides a mechanism
for sending either sequence.
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