<s>
The	O
Apollo	B-Device
Abort	I-Device
Guidance	I-Device
System	I-Device
(	O
AGS	O
,	O
also	O
known	O
as	O
Abort	O
Guidance	O
Section	O
)	O
was	O
a	O
backup	O
computer	O
system	O
providing	O
an	O
abort	O
capability	O
in	O
the	O
event	O
of	O
failure	O
of	O
the	O
Lunar	O
Module	O
's	O
primary	O
guidance	O
system	O
(	O
Apollo	O
PGNCS	O
)	O
during	O
descent	O
,	O
ascent	O
or	O
rendezvous	O
.	O
</s>
<s>
The	O
AGS	O
was	O
designed	O
by	O
TRW	O
independently	O
of	O
the	O
development	O
of	O
the	O
Apollo	B-Application
Guidance	I-Application
Computer	I-Application
and	O
PGNCS	O
.	O
</s>
<s>
Although	O
not	O
as	O
accurate	O
as	O
the	O
gimbaled	O
IMU	O
,	O
it	O
provided	O
satisfactory	O
accuracy	O
with	O
the	O
help	O
of	O
the	O
optical	O
telescope	O
and	O
rendezvous	O
radar	B-Application
.	O
</s>
<s>
The	O
Abort	B-Device
Guidance	I-Device
System	I-Device
included	O
the	O
following	O
components	O
:	O
</s>
<s>
Because	O
the	O
memory	O
had	O
a	O
serial	B-Protocol
access	I-Protocol
it	O
was	O
slower	O
than	O
AGC	O
,	O
although	O
some	O
operations	O
on	O
AEA	O
were	O
performed	O
as	O
fast	O
or	O
faster	O
than	O
on	O
AGC	O
.	O
</s>
<s>
It	O
was	O
an	O
18-bit	O
machine	O
,	O
with	O
17	O
magnitude	O
bits	O
and	O
a	O
sign	B-Algorithm
bit	I-Algorithm
.	O
</s>
<s>
Data	O
words	O
were	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
and	O
in	O
fixed-point	O
form	O
.	O
</s>
<s>
The	O
AEA	O
instruction	O
format	O
consisted	O
of	O
five-bit	O
instruction	B-Language
code	I-Language
,	O
index	O
bit	O
and	O
a	O
12-bit	O
address	O
.	O
</s>
<s>
ADD	O
:	O
The	O
contents	O
of	O
memory	O
location	O
are	O
added	O
to	O
Accumulator	B-General_Concept
A	O
.	O
</s>
<s>
ADZ	O
(	O
Add	O
and	O
Zero	O
)	O
:	O
The	O
contents	O
of	O
memory	O
are	O
added	O
to	O
Accumulator	B-General_Concept
A	O
.	O
</s>
<s>
SUB	O
(	O
Subtract	O
)	O
:	O
The	O
contents	O
of	O
memory	O
are	O
subtracted	O
from	O
Accumulator	B-General_Concept
A	O
.	O
</s>
<s>
SUZ	O
(	O
Subtract	O
and	O
Zero	O
)	O
:	O
The	O
contents	O
of	O
memory	O
are	O
subtracted	O
from	O
Accumulator	B-General_Concept
A	O
.	O
</s>
<s>
MPY	O
(	O
Multiply	O
)	O
:	O
The	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
are	O
multiplied	O
by	O
the	O
contents	O
of	O
memory	O
.	O
</s>
<s>
The	O
most	O
significant	O
part	O
of	O
the	O
product	O
is	O
placed	O
in	O
the	O
Accumulator	B-General_Concept
A	O
,	O
the	O
least	O
significant	O
part	O
is	O
placed	O
in	O
Register	O
Q	O
.	O
</s>
<s>
MPR	O
(	O
Multiply	O
and	O
Round	O
)	O
:	O
Identical	O
to	O
MPY	O
instruction	O
,	O
the	O
most	O
significant	O
part	O
of	O
the	O
product	O
in	O
Accumulator	B-General_Concept
A	O
is	O
rounded	O
by	O
adding	O
one	O
to	O
the	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
if	O
bit	O
1	O
of	O
Q	O
Register	O
equals	O
one	O
.	O
</s>
<s>
DVP	O
(	O
Divide	O
)	O
:	O
The	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
and	O
Register	O
Q	O
that	O
form	O
a	O
dividend	O
are	O
divided	O
by	O
the	O
contents	O
of	O
memory	O
.	O
</s>
<s>
The	O
quotient	O
is	O
placed	O
in	O
Accumulator	B-General_Concept
A	O
and	O
rounded	O
unless	O
the	O
rounding	O
would	O
cause	O
overflow	O
.	O
</s>
<s>
COM	O
(	O
Complement	O
Accumulator	B-General_Concept
)	O
:	O
The	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
are	O
replaced	O
with	O
their	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
.	O
</s>
<s>
If	O
the	O
contents	O
of	O
the	O
Accumulator	B-General_Concept
A	O
are	O
positive	O
,	O
zero	O
or	O
minus	O
one	O
,	O
the	O
contents	O
remain	O
unchanged	O
.	O
</s>
<s>
CLA	O
(	O
Clear	O
and	O
Add	O
)	O
:	O
The	O
Accumulator	B-General_Concept
A	O
is	O
loaded	O
from	O
memory	O
.	O
</s>
<s>
STO	O
(	O
Store	O
Accumulator	B-General_Concept
)	O
:	O
The	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
are	O
stored	O
in	O
memory	O
.	O
</s>
<s>
The	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
remain	O
unchanged	O
.	O
</s>
<s>
ALS	O
N	O
(	O
Arithmetic	O
Left	O
Shift	O
)	O
:	O
The	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
are	O
shifted	O
left	O
N	O
places	O
.	O
</s>
<s>
LLS	O
N	O
(	O
Long	O
Left	O
Shift	O
)	O
:	O
The	O
contents	O
of	O
Accumulator	B-General_Concept
A	O
and	O
bits	O
1	O
-	O
17	O
of	O
Q	O
Register	O
are	O
shifted	O
left	O
as	O
one	O
register	O
N	O
places	O
.	O
</s>
<s>
The	O
sign	O
of	O
Q	O
Register	O
is	O
made	O
to	O
agree	O
with	O
sign	O
of	O
Accumulator	B-General_Concept
A	O
.	O
</s>
<s>
TMI	O
(	O
Transfer	O
on	O
Minus	O
Accumulator	B-General_Concept
)	O
:	O
The	O
next	O
instruction	O
is	O
taken	O
from	O
memory	O
if	O
the	O
contents	O
of	O
the	O
Accumulator	B-General_Concept
A	O
are	O
negative	O
.	O
</s>
<s>
INP	O
(	O
Input	O
)	O
:	O
The	O
contents	O
of	O
input	O
register	O
specified	O
by	O
address	O
are	O
placed	O
in	O
Accumulator	B-General_Concept
A	O
.	O
</s>
<s>
OUT	O
(	O
Output	O
)	O
:	O
The	O
contents	O
of	O
the	O
Accumulator	B-General_Concept
A	O
are	O
placed	O
in	O
output	O
register	O
specified	O
by	O
address	O
.	O
</s>
<s>
First	O
design	O
ideas	O
of	O
the	O
Abort	B-Device
Guidance	I-Device
System	I-Device
did	O
not	O
include	O
the	O
use	O
of	O
the	O
computer	O
but	O
rather	O
a	O
sequencer	O
without	O
any	O
navigation	O
capability	O
.	O
</s>
<s>
There	O
was	O
also	O
a	O
set	O
of	O
computations	O
that	O
had	O
to	O
be	O
performed	O
every	O
40	O
ms	O
(	O
engine	O
commands	O
,	O
external	O
signal	O
sampling	B-Algorithm
,	O
attitude	O
control	O
,	O
etc	O
.	O
</s>
<s>
radar	B-Application
data	O
processing	O
,	O
calculation	O
of	O
orbital	O
parameters	O
,	O
computation	O
of	O
rendezvous	O
sequence	O
,	O
calibration	O
of	O
IMU	O
sensors	O
,	O
etc	O
.	O
)	O
</s>
