Poll Sequence Format - HP 262SA Reference Manual

Data Communications
The device ID is set using the
((Devi ce I D"
field of the datacomm configuration menu described
in table 3-4.
The group IDs for polling and selecting are set using the
((PGr oup I D"
and
((SGr oup I D"
fields of
the datacomm configuration menu described in table 3-4. To use group functions, all terminals
in a group must be ((daisy-chained" together (physically connected to one another so as to share
the same modem or hardwired line).
POLLING.
The computer enables data transmission by each terminal by ((polling" each
terminal, individually. The computer may poll the terminals in any order.
Figure 7-11 illustrates the general format of a poll sequence for both asynchronous and
synchronous configurations.
ASYNCHRONOUS
<Ey-><PAD>t<GROUP ID><GROUP ID><DEV ID><DEV
ID><~><PAD>
SYNCHRONOUS
<\.><Ey-><PAD>t<\.><GROUP ID><GROUP ID><DEV ID><DEV
ID><~><PAD>
• 3 or more SYN characters.
tThese PAD characters are optional, but if present, should be FF hex).
The GROUP 10 is used for polling.
Figure 7-11. Poll Sequence Format
GROUP POLLING.
To reduce the time and programming required to poll each terminal on a
communication line you can perform a group poll. This allows all of the terminals in a group
(terminals having the same group ID) with queued output data to respond to a single poll
sequence. The terminals respond in order according to their position on the communication line
(with those at the far end of the communication line being held off until all terminals ahead of
them on the string have completed their data transfers). When the last terminal with queued
output data is finished with its transmission it sends an <EOT> to the host computer to
indicate that the group transmissions are completed.
The group poll sequence is similar to the normal poll sequence. The character
U
(042
octaD is used
in place of the device ID characters. For example, to poll all of the terminals in group A you
could use the sequences illustrated in figure 7-12.
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