The Control
Start
field
(bit positions
15-20,
21,
or 22)
points to
the
beginning
of the memory region controlled by
the
registers
to
be
loaded.
The
significance
of
this field
is
different
for the 5 modes of MMC
operations
and
is
des-
cribed
within
each
mode below.
Affected:
(R),
(Ru
1),
memory control
storage
T raps: Instruction
exception,
nonallowed
operation.
LOADING
THE
MEMORY
MAP
CONTROL IMAGE
Each word
of
the
memory map control image
contains
either
four
8-bit
page
addresses or two
11-bit
extended
page
ad-
dresses, as
illustrated
below:
T ypi
cal memory map control image word
(8-bit
format):
Typical memory map control image word
(ll-bit
format):
Depending upon the memory map control image format,
the
instruction format
is
one
of the following:
LMAP
LOAD
MAP
(~-bit
format)
LMAPRE
LOAD
MAP
REAL
EXTENDED
(11-bit
format)
Depending upon
the
type
of
addressing,
the
format
of
regis-
ter
R contents
is
one
of
the following:
IfMA=O;
Map
lmag:e
Address
If
,AI-A
= 1 and
MM
=
0;
Map
~age
Real
Exte~ded
Address
98 Control Instructions
For
either
memory map format
and
either
type
of
addressing,
the
contents
of
register
Ru
1
are:
MEMORY
MAP
LOADING
PROCESS
The
initial
map image address (in
register
R)
is
the
virtual
address
of
the
first word
of
the memory map control image.
The
initial
count,
as
contained
in
register
Ru
1 specifies
the
word length of
the
control image
to
be
loaded.
A word
count
of
64
(for
8-bit
format)
or
128 (for
ll-bit
format)
is
sufficient
to load an
entire
block
of
256 memory map
con-
trol registers. The memory map control registers
are
treated
as
a
circular
set,
with
the
first register following the last;
thus,
a word count
greater
than
64
(8-bit
format) or 128
(ll-bit
format) causes the first registers
to
be
overwritten.
The
initial
value
of
the
control
start
field of register
Ru
1
points to
the
first
page
(512 words)
of
virtual
addresses
that
are
to
be
controlled
by
the
memory map control image being
loaded.
The memory map control image
is
loaded into the
memory map control registers
one
word
at
a
time.
As
the
contents
of
each
word
are
loaded into
either
two
orfourmem-
ory map control
registers,
the
map image address
is
incre-
mented by
1,
the
word count
is
decremented
by
1,
and
the
value
in
the
control
start
field is
incremented
either
byfour
(if
the
memory map control image
is
in
the
8-bit
format)
or
by two (if
the
memory map control image
is
in the
l1-bit
format). The loading process continues until the word count
is
reduced
to
zero.
When
the
load process
is
completed,
the
map image address
of
register
R contains a
value
equal
to the
sum
of
the
initial
map image address plus
the
initial
word
count,
the
word
count
of
register
Ru
1 has a va lue
of
zero,
and the control
start
field
of
register
Ru
1 contains a
value
equal
to
the
sum
of
the
initial
contents plus four
or
two times the
initial
word
count.
LOADING
THE
ACCESS
PROTECTION
CONTROLS
CONTROL IMAGE
Each
access
protection
control image word contains sixteen
2-bit
fields;
or,
the
access
protection
codes for
16
consecu-
tive
pages
of
virtual memory. Thus,
the
access
protection
control image for 128K word (256 page) virtual memory
is
contained
within
16
contiguous memory
locations,
desig-
nated
as
the
access
protection
control image
area.
The fermat
of
c
typical
access
protection control image
word is:
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