6100 BSC Programming Manual

Writing Applications that Use 6100 BSC
Transferring Data
Once a line bid has occurred, the stations begin to exchange
data. Usually the transmitting station makes a series of WRITE
requests, as in Figure 3-5. Each request sends a message or a
block, and awaits an acknowledgement. A WRITE request completes
when the acknowledgement arrives. Notice that in the figure, the
first WRITE request includes the line bid.
To acknowledge a block and receive the next one, the receiving
station makes a READ request. In sending acknowledgements,
BSC alternates between ACK 0 and ACK 1. The READ request
completes when the next transmission has arrived. Notice that
in Figure 3-5, the first READ request accepts the line bid
and reads the first block. The second request acknowledges the
first block and reads the second one.
If the transmitting station is temporarily unable to send data,
it can make a CONTROL request with the TTD option. (See the
discussion of TTD in Section 1.) The request sends a TTD
sequence and awaits an acknowledgement, normally NAK. The
application can make repeated CONTROL TTD requests, then
finally make a WRITE request when it is ready to transmit.
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