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Data Communications
Multipoint Operating States
A terminal in an HP Multipoint configuration is always in one of the following three operating
states:
Control Mode:
Text-In Mode:
Text-Out Mode:
In this operating state the terminal is either waiting to be polled/selected
or is in the process of being polled/selected.
In this operating state the terminal has been selected and is actually
receiving data. The terminal remains in Text-In Mode until it sends or
receives an <EOT>, at which time it then switches back to Control Mode.
In this operating state the terminal has been polled and is actually
transmitting data. The terminal remains in Text-Out Mode until:
1. It sends or receives an <EOT>; or
2. It passes control to a subsequent terminal in the daisy-chained group.
In either case the terminal then switches back to Control Mode.
Table 7-7 summarizes the block protocol control characters used in these modes.
HP Multipoint Protocol Control Sequences
The HP multipoint protocol requires specific control sequences to acknowledge text block
transfers, terminate text transfers, or to inform the sender or receiver of status changes. These
sequences consist of one or more data link control characters. A list of these control characters
is presented in table 7-6. A summary of the uses of these characters is presented in table 7-7.
Figure 7-20 illustrates the operation of the various control characters used in the HP multi-
point protocol.
7-39
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