Alto Hardware
Manual
4
5
6
7
Task-specific
"'MD
...
MOUSE
"'DISP
Section
2:
Microprocessor
Performs different functions in different tasks.
Memory
data
Bus[12-15]+-
MOUSE;
BUS[O-13]+-
-1
IR[8-15],
possibly sign extended (see section 3.5)
5
RName+-
is
not logically a source,
but
because
it
is
gated to the bus during
both
reading "and writing,
it
is
included in the source specifiers. Loading R forces the
BUS
to 0 so that
an
ALU
function
of
0
and
T may
be
executed simultaneously.
The
bus has the property that
if
more than one source is gated to
it
during a single microinstruction,
it
computes the
AND
of
the source values. This is true regardless
of
the means by which the sources are
enabled
(BS,
Fl,
or
F2).
This bus source decoding
is
not performed
if
Fl=7
or
F2=7.
These functions use the
BS
field to provide
part
of
the address to the constant
ROM.
SPECIAL
FUNCTIONS
The
two function fields specify the address modifiers, register load signals (other than those for
R,
S,
L,
M
and
T),
and other special conditions required in the processor.
The
first eight conditions specified by
each field (except
BLOCK)
are interpreted identically
by
all tasks,
but
the interpretation
of
the second
eight depends
on
the active task. The task-independent functions are given below; the task-specific
functions are included with the task descriptions.
FUNCTION
1:
Fl
o
1
2
3
4
5
6
7
NAME
MAR'"
TASK
BLOCK
"'L
LSH
1
"'L
RSH
1
"'L
LCY8
"'CONSTANT
MEANING
No
Activity
Load
MAR
from
ALU
output; start main memory reference (see section
2.3).
Switch tasks
if
higher priority wakeup
is
pending (see section 2.4).
Disable the current task until re-enabled
by
a hardware-generated
condition. Note: this function
is
reserved by convention only; it is not
done by the microprocessor.
SHIFTER
OUTPUT
will
be
L shifted left
one
place*
SHIFTER
OUTPUT
will
be
L shifted right
one
place*
SHIFTER
OUTPUT
will
be
L rotated left 8 places*
Put
on
the bus the constant from the constant
ROM
location addressed by
RSELECT.BS
*Modified
by
DNS
(DO
Novel Shifts) function, and
MAGIC
function. L
LSH
land
L
RSH
1
ordinarily shift a zero into the vacated
bit
position.
FUNCTION
2:
F2
NAME
MEANING
0
No
Activity
1
BUS=O
NEXT'"
NEXT
OR
(if
(BUS=O)
then 1 else 0).
2
SH(O
NEXT'"
NEXT
OR
(if
(SHIFTER
OUTPUT(O)
then
1 else 0).*
3
SH=O
NEXT'"
NEXT
OR
(if
(SHIFTER
OutPUT=O)
then
1 else 0).*
4
BUS
NEXT'"
NEXT
OR
Bus[6-15]
To Next Page
Loading...
Need help?
General
