In
this
manual, B
registers
are individually referred to
by
the
letter
B
and
a
2-digit
octal subscript in the range
00
through
77.
Instructions
reference
B
registers
by
allowing
specification
of the octal subscript
as
the jk designator
as
described in section 4 of
this
manual.
The
only B
register
to
which
an
implicit
reference
is
made
is
the
Boo
register.
On
execution of the return
jump
instruction
(007),
register
Boo
is
set
to
the next instruction parcel address
and
a
branch
to
an
address specified
by
ijkm
occurs.
Upon
receiving
control,
the called routine will
con-
ventionally save (Boo)
so
that
the
Boo
register
will
be
free for the
called routine to
initiate
return
jumps
of
its
own.
When
a called routine
wishes to return to
its
caller,
it
restores the saved address
and
executes
a
005
instruction.
This
instruction,
which
is
a branch to (Bjk), causes
the address saved in
Bjk
to
be
entered into P
as
the address of the next
instruction parcel to
be
executed.
FUNCTIONAL
UNITS
Instructions other than simple transmits or control operations are
performed
by
hardware organizations
known
as
functional
units.
Each
unit
implements
an
algorithm or a portion of the
instruction
set.
Units are
independent; a
number
of functional units
can
be
in operation
at
the
same
time.
A functional unit receives operands
from
registers
and
delivers the
result
to a
register
when
the function
has
been
performed.
The
units operate
essentially
in three-address
mode
with source
and
destination addressing
limited to
register
designators.
All
functional units perform
their
algorithms in a fixed
amount
of time;
no
delays are possible
once
the operands
have
been
delivered to the
unit.
The
amount
of time required
from
delivery of the operands to the
unit
to
the completion of the calculation
is
termed
the "functional
unit
time"
and
is
measured
in 12.5 nsec clock periods.
The
functional units
~re
fully
segmented.
This
means
that
a
new
set
of operands for
any
computation
may
enter a functional unit
each
2240004
3-10
E
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