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 groupfunctions, 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
accordingto
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.
7-25
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