Sage II - Mechanical Changes; General Mechanical Notes

sAcE
rr
SERVICE
MANUAL
[1.0]
ERROR
LOOKUP
LIST
EXCEPTION
ERR0RS
(cont)
BUS
ERROR
DUE
TO ADDRESSIXG
NOHEXISTANT
T,fEUORY
LOCATIONS
Address
error
I,rlhenever
a
memory address
ls
addressed
whlch
is
not
a
decoded
address ln
the
SAGE
II
menory
map
there
is no
DTACK-
generated
whtch
causes
a
bus tlmeout
error
as
descrlbed
above.
This
allows
an
orderly
recovery
from
the addresslng
of
any nonexlstent
memory
locatlons.
A DTACK- is
generated
for
all
locatlons
in
the
SAGE
II memory
nap
which
means that lf
the
system
had
only
128K
and a
locatlon
between
128K &
512K
were
addressed,
there
would
be
no
lndlcatlon.
To
solve the
problem
the
bank
enables
for
banks
1, 2, &
3
are fed
through
an nonLnvertlng
open
collector
buffer
(Ul4)
to the
bus
error
lnput
of the
processor
through a
dlp
shunt.
Wlth
the
proper
connectlons ln
the
dlp
shunt the
addresslng
of
any
locatlon
ln
banks
l,
2, or
3
can cause a
bus
error
lndicatlng
an lnvalld
memory
address.
The
processor
attempted
to
access
a
word
or
long
word
on an
odd address.
Addltlonal
lnformation
ls
displayed
with thls
^rror:
ttFunctlon
:xxxx
Access
:xxxxxxxx
Instr :xxxxtt
Function
0-2 .
3.
Access
Ins
tr
is
a
4
diglt word
r^rlth
blts
set:
.are the state
of the
processor
function
code outputs FCO,FCl
and
FC2
.is 0
for
an l-nstructlon,
I
for
not
an lnstruction.
4
..1s
0
for
wrlte,
I
for read.
ls
the
8
digtt
address
of
the attempt.
is the
4
digit lnstructlon
word
executed
76