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6
ST
A
Tus
Commands
There
are
two
`nodes'
in
the
status
circuitry
.
The
OPERation
node
shows
things
that
can
happen
during
normal
operation.
The
QUEStionable
node
shows
error
conditions
.
Each
node
of
the
status
circuitry
has
ve
registers:
A
condition
register
(CONDition),
which
contains
the
current
status
.
This
register
is
updated
continuously
.
It
is
not
changed
by
having
its
contents
read.
The
event
register
(EVENt),
which
contains
the
output
from
the
transition
registers
.
The
contents
of
this
register
are
cleared
when
it
is
read.
A
positive
transition
register
(PTRansition),
which,
when
enabled,
puts
a
1
into
the
event
register
,
when
the
corresponding
bit
in
the
condition
register
goes
from
0
to
1.
The
power-on
condition
for
this
register
is
for
all
the
bits
to
be
enabled.
A
negative
transition
register
(NTRansition),
which,
when
enabled,
puts
a
1
into
the
event
register
,
when
the
corresponding
bit
in
the
condition
register
goes
from
1
to
0.
The
power-on
condition
for
this
register
is
for
all
the
bits
to
be
disabled.
The
enable
register
(ENABle),
which
enables
changes
in
the
event
register
to
aect
the
Status
Byte
.
The
status
registers
for
the
polarization
controller
are
organized
as
shown:
Remote
Commands
6-23