<s>
The	O
Processor	O
Technology	O
VDM-1	B-Device
,	O
for	O
Video	B-Device
Display	I-Device
Module	I-Device
,	O
was	O
the	O
first	O
video	B-Device
card	I-Device
for	O
S-100	B-Architecture
bus	I-Architecture
computers	O
.	O
</s>
<s>
Created	O
in	O
1975	O
,	O
it	O
allows	O
an	O
S-100	B-Architecture
machine	O
to	O
produce	O
its	O
own	O
display	O
,	O
and	O
when	O
paired	O
with	O
a	O
keyboard	O
and	O
their	O
3P+S	B-Architecture
card	O
,	O
it	O
eliminates	O
the	O
need	O
for	O
a	O
separate	O
video	B-General_Concept
terminal	I-General_Concept
.	O
</s>
<s>
Using	O
a	O
7	O
x	O
9	O
dot	B-General_Concept
matrix	I-General_Concept
and	O
ASCII	B-Protocol
characters	I-Protocol
,	O
it	O
produces	O
a	O
64-column	O
by	O
16-row	O
text	O
display	O
.	O
</s>
<s>
The	O
VDM-1	B-Device
is	O
a	O
complex	O
card	O
and	O
was	O
soon	O
replaced	O
by	O
an	O
increasing	O
number	O
of	O
similar	O
products	O
from	O
other	O
companies	O
.	O
</s>
<s>
In	O
September	O
1973	O
,	O
the	O
cover	O
article	O
of	O
Radio	B-Application
Electronics	I-Application
magazine	O
was	O
Don	O
Lancaster	O
's	O
"	O
Build	O
a	O
TV	O
Typewriter	O
"	O
,	O
which	O
allows	O
users	O
to	O
type	O
characters	O
on	O
a	O
keyboard	O
and	O
have	O
them	O
appear	O
on	O
a	O
conventional	O
television	O
.	O
</s>
<s>
Throughout	O
1973	O
,	O
Felsenstein	O
had	O
been	O
looking	O
for	O
a	O
low-cost	O
terminal	O
for	O
the	O
Community	O
Memory	O
bulletin	B-Application
board	I-Application
system	I-Application
.	O
</s>
<s>
He	O
had	O
designed	O
the	O
Pennywhistle	B-Device
modem	I-Device
to	O
address	O
the	O
need	O
for	O
remote	O
access	O
at	O
a	O
price	O
under	O
$100	O
,	O
but	O
the	O
terminal	O
that	O
they	O
hooked	O
it	O
up	O
to	O
still	O
cost	O
$1500	O
.	O
</s>
<s>
Felsenstein	O
began	O
designing	O
a	O
printed	O
circuit	O
board	O
that	O
would	O
combine	O
the	O
video	O
output	O
of	O
the	O
TV	O
Typewriter	O
with	O
1024	O
bytes	O
of	O
memory	O
so	O
it	O
could	O
hold	O
a	O
page	O
of	O
text	O
in	O
ASCII	B-Protocol
format	O
and	O
send	O
it	O
to	O
a	O
video	O
monitor	O
.	O
</s>
<s>
As	O
soon	O
as	O
the	O
prototype	O
was	O
ready	O
,	O
Steve	O
Dompier	O
began	O
porting	O
Star	B-Application
Trek	I-Application
to	O
it	O
,	O
replacing	O
its	O
serial	O
output	O
with	O
a	O
more	O
game-like	O
display	O
to	O
produce	O
Trek-80	O
.	O
</s>
<s>
As	O
reviews	O
of	O
the	O
era	O
noted	O
,	O
an	O
Altair	O
compatible	O
machine	O
equipped	O
with	O
a	O
keyboard	O
,	O
the	O
VDM-1	B-Device
,	O
and	O
an	O
appropriate	O
monitor	O
(	O
from	O
Radio	O
Shack	O
)	O
cost	O
less	O
than	O
a	O
typical	O
smart	O
terminal	O
of	O
the	O
era	O
.	O
</s>
<s>
Felsenstein	O
initially	O
wanted	O
to	O
use	O
a	O
different	O
processor	O
,	O
but	O
eventually	O
concluded	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
was	O
the	O
best	O
solution	O
.	O
</s>
<s>
The	O
VDM-1	B-Device
had	O
16	O
rows	O
simply	O
because	O
64	O
x	O
16	O
=	O
1	O
,	O
024	O
,	O
the	O
amount	O
of	O
memory	O
on	O
the	O
card	O
.	O
</s>
<s>
The	O
VDM-1	B-Device
uses	O
a	O
single	O
slot	O
in	O
the	O
S-100	B-Architecture
backplane	O
,	O
but	O
is	O
so	O
large	O
it	O
covers	O
adjacent	O
slots	O
in	O
most	O
machines	O
.	O
</s>
<s>
The	O
front	O
side	O
of	O
the	O
board	O
was	O
crammed	O
with	O
components	O
,	O
including	O
eight	O
91L02A	O
1,024	O
bit	O
static	B-Architecture
RAMs	I-Architecture
,	O
to	O
the	O
point	O
that	O
there	O
was	O
not	O
enough	O
room	O
left	O
for	O
the	O
required	O
electrical	O
traces	O
.	O
</s>
<s>
The	O
display	O
is	O
black	O
and	O
white	O
,	O
and	O
the	O
hardware	O
includes	O
the	O
ability	O
to	O
support	O
inverse	B-General_Concept
video	I-General_Concept
,	O
which	O
they	O
refer	O
to	O
as	O
"	O
cursor	O
bytes	O
"	O
,	O
by	O
setting	O
the	O
high	O
bit	O
on	O
the	O
character	O
byte	O
.	O
</s>
<s>
One	O
oddity	O
of	O
the	O
system	O
is	O
that	O
the	O
character	O
graphics	O
were	O
supplied	O
in	O
ROM	B-Device
,	O
and	O
there	O
are	O
several	O
versions	O
of	O
the	O
ROMs	O
with	O
different	O
glyphs	O
.	O
</s>
