Datron 4708 User Handbook Manual page 63

Operational
Sequence
Guidelines
Most
interface
communication
tasks require
sequences of coded
messages
to
be sent over the
interface.
Many
controllers assign
a
single
programming
instruction to
a complete sequence, so
it
is
advisable
to
study the available controller capabilities care-
fully
before attempting
to
program
a system.
Because
the
IEEE
Std488
(1978) allows a
certain latitude in
bus
protocol, consid-
erable differences
may
be found between programming
instruc-
tions
and
operating
sequences
from one
make
of
controller to
another. Consequently, the
following sequences
are
recom-
mendations
only.
Data Transfer
UNL
Inhibits
all
current listeners
LADj
Each
address sent enables a specific
device
to
receive future data
bytes.
L AD^
More
than
one
address
may
be
sent
if
multiple
listeners desired.
TAD
The
address
sent
enables a
specific
device
to
send
data.
The 4708 must be
already
programmed
to
prepare data.
DAB^
Data
bytes sent
by currently-enabled
talkers to
all
currently-enabled
listeners.
DAB„
UNT
Disables the talker
on
receipt
of
the
last
character.
pUNL
=
unlisten
—
LAD
=
listen
address of
specific
device
TAD =
talk
address of
specific
device
DAB
=
data bytes
Lunt
=
untalk
—
Untalk
It is
highly desirable
that
a
sequence which
causes a device
to
be
addressed
as
a
talker
should be terminated
by an
'untalk'
com-
mand.
Serial Poll
UNL
Inhibits
all
current
listeners
SPE
Puts
interface into
serial
poll
mode
during
which
all
devices
send
status
instead of data
when
addressed.
TAD^
Enables a
specific device
to
send
status.
Within
this
loop, device should be sequentially enabled.
SBN
)
Status byte sent
by
enabled device:
or
)
If
SBN,
loop should be repeated.
If
SBA
sent,
the
SB
A
)
enabled device
is
identified as
having
sent
SRQ
and
will
automatically
remove
it.
SPD
Disables
serial poll
mode.
UNT
Disable
last talker
pSPE
SPD
SBN
l-SBA
Serial poll
enable
-
Serial poll disable
Status byte negative
where
bit
7
=
0
Status byte affirmative
where
bit
7
=
1
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