6100 BSC Programming Manual

Writing Applications that Use 6100 BSC
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| |
| |
| Local Station Remote Station |
| |
| WRITE . \ |
| requests . <-------- ACK n | READ |
| . | requests |
| / | |
| WRITE | msg ---------> / |
| request | \ |
| | <-------- ACK n | READ |
| \ | request |
| / | |
| WRITEREAD | msg ---------> / |
| request | \ |
| | < ------- msg | WRITEREAD request |
| \ | (conversational |
| / | reply) |
| | ACK n or msg --> | |
| READ to | / |
| send ACK, | \ |
| WRITE to | <-- ACK n or msg | READ if msg arrived, |
| send msg | | WRITE if ACK arrived |
| \ |
| |
| |
| The underscore shows the information applications |
| supply and receive. In each case, the information |
| resides in the text field of the request/response |
| buffer (see Figure 3-9). Items not underscored--for |
| example, most control sequences--are supplied and |
| received by the protocol, not by the application. |
| |
| Notice that after the local station receives a |
| conversational reply, its response--READ or WRITE-- |
| determines whether the stations change roles. If it |
| issues a READ, it enters READ state and the other |
| station enters WRITE state. If it issues a WRITE, it |
| remains in WRITE state and the other station remains |
| in READ state. When a WRITEREAD completes, you can |
| tell whether an ACK or a message arrived by checking |
| the Text In field in the response buffer (see |
| WRITEREAD, below). |
| |
| |
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Figure 3-7. Conversational Reply
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