<s>
The	O
COSMAC	B-Device
Elf	I-Device
was	O
an	O
RCA	B-General_Concept
1802	I-General_Concept
microprocessor-based	O
computer	O
described	O
in	O
a	O
series	O
of	O
construction	O
articles	O
in	O
Popular	O
Electronics	O
magazine	O
in	O
1976	O
and	O
1977	O
.	O
</s>
<s>
The	O
system	O
was	O
a	O
very	O
early	O
single-board	O
personal	B-Device
computer	I-Device
.	O
</s>
<s>
It	O
was	O
operated	O
without	O
built-in	O
ROMs	O
and	O
programs	O
were	O
entered	O
directly	O
with	O
help	O
of	O
the	O
CPU	B-Device
integrated	O
DMA	O
using	O
8	O
toggle	O
switches	O
and	O
an	O
Input	O
push	O
button	O
.	O
</s>
<s>
It	O
featured	O
two	O
hexadecimal	O
LED	O
displays	O
for	O
byte	B-Application
data	O
value	O
output	O
and	O
a	O
set	O
of	O
8	O
toggle	O
switches	O
for	O
input	O
.	O
</s>
<s>
(	O
a	O
hexadecimal	O
keypad	B-Device
was	O
an	O
optional	O
extension	O
)	O
The	O
base	O
configuration	O
had	O
256	O
bytes	B-Application
of	O
RAM	B-Architecture
,	O
but	O
expansion	O
projects	O
could	O
raise	O
that	O
to	O
a	O
power	O
of	O
two-based	O
memory	O
store	O
,	O
with	O
an	O
upper	O
limit	O
of	O
64K	O
address	O
space	O
.	O
</s>
<s>
A	O
simple	O
circuit	O
used	O
the	O
DMA	O
feature	O
of	O
the	O
1802	O
to	O
permit	O
entry	O
of	O
programs	O
and	O
data	O
into	O
RAM	B-Architecture
through	O
the	O
toggle	O
switches	O
.	O
</s>
<s>
Entering	O
a	O
byte	B-Application
via	O
the	O
toggle	O
switches	O
and	O
pressing	O
the	O
"	O
input	O
"	O
button	O
would	O
enter	O
a	O
byte	B-Application
into	O
RAM	B-Architecture
and	O
display	O
it	O
on	O
the	O
pair	O
of	O
hex	O
LEDs	O
,	O
then	O
advance	O
the	O
DMA	O
counter	O
to	O
the	O
next	O
location	O
.	O
</s>
<s>
The	O
fourth	O
article	O
of	O
the	O
series	O
presented	O
modifications	O
to	O
use	O
a	O
companion	O
RCA	O
1861	O
“	O
Pixie	O
”	O
video	B-General_Concept
generator	O
IC	O
(	O
CDP1861	O
)	O
.	O
</s>
<s>
The	O
Pixie	O
required	O
a	O
1.76MHz	O
clock	O
,	O
and	O
since	O
that	O
was	O
an	O
uncommon	O
crystal	O
frequency	O
,	O
usually	O
a	O
readily	O
available	O
3.579545MHz	O
colorburst	O
crystal	O
was	O
instead	O
used	O
in	O
a	O
separate	O
oscillator	O
circuit	O
with	O
a	O
divide-by-two	O
circuit	O
to	O
drive	O
the	O
clock	O
inputs	O
of	O
both	O
the	O
microprocessor	B-Architecture
and	O
Pixie	O
.	O
</s>
<s>
Monochrome	O
video	B-General_Concept
output	O
(	O
with	O
timing	O
roughly	O
approximating	O
NTSC	O
standard	O
)	O
could	O
be	O
generated	O
using	O
DMA	O
operations	O
interleaved	O
with	O
carefully	O
arranged	O
1802	O
opcodes	O
as	O
instructions	O
in	O
software	O
.	O
</s>
<s>
By	O
changing	O
the	O
placement	O
of	O
instructions	O
in	O
the	O
video	B-General_Concept
display	O
control	O
and	O
interrupt	O
routines	O
,	O
pixel	O
rows	O
could	O
be	O
repeated	O
to	O
obtain	O
lower	O
resolutions	O
,	O
allowing	O
the	O
video	B-General_Concept
display	O
to	O
be	O
used	O
with	O
256	O
bytes	B-Application
of	O
RAM	B-Architecture
(	O
64×32	O
square	O
pixels	O
)	O
.	O
</s>
<s>
A	O
one-bit	O
output	O
from	O
the	O
microprocessor	B-Architecture
,	O
the	O
Q	O
line	O
,	O
could	O
be	O
driven	O
by	O
software	O
to	O
produce	O
sounds	O
through	O
an	O
attached	O
speaker	O
,	O
to	O
save	O
programs	O
in	O
RAM	B-Architecture
to	O
a	O
cassette	O
recorder	O
,	O
and	O
for	O
serial	O
I/O	O
output	O
.	O
</s>
<s>
Branch	O
instructions	O
in	O
the	O
1802	O
instruction	O
set	O
could	O
read	O
the	O
state	O
of	O
the	O
EF1	O
through	O
EF4	O
single	O
bit	O
value	O
input	O
lines	O
,	O
which	O
were	O
used	O
to	O
read	O
the	O
'	O
I	O
 '	O
keypad	B-Device
(	O
input	O
)	O
momentary	O
pushbutton	O
(	O
typically	O
EF4	O
)	O
,	O
programs	O
from	O
the	O
cassette	O
recorder	O
through	O
interface	O
circuitry	O
,	O
serial	O
I/O	O
input	O
,	O
and	O
input	O
from	O
peripherals	O
such	O
as	O
a	O
light	O
pen	O
.	O
</s>
<s>
The	O
original	O
Elf	O
computers	O
were	O
essentially	O
home-built	O
versions	O
of	O
the	O
RCA	O
Microkit	O
,	O
Microtutor	O
I	O
and	O
Microtutor	O
II	O
,	O
which	O
were	O
RCA	O
's	O
demonstration	O
boards	O
for	O
their	O
CDP1801	O
2-chip	O
predecessor	O
and	O
single-chip	O
CDP1802	B-General_Concept
microprocessors	B-Architecture
.	O
</s>
<s>
Enhanced	O
kits	O
such	O
as	O
the	O
Netronics	B-Device
Elf	I-Device
II	I-Device
and	O
Quest	O
Super	O
Elf	O
added	O
built-in	O
features	O
such	O
as	O
keypads	B-Device
for	O
data	O
entry	O
,	O
serial	O
I/O	O
,	O
cassette	O
interface	O
,	O
and	O
the	O
CDP1861	O
"	O
Pixie	O
"	O
video	B-General_Concept
chip	I-General_Concept
.	O
</s>
<s>
RCA	O
later	O
introduced	O
their	O
own	O
similarly	O
expanded	O
version	O
as	O
the	O
COSMAC	B-Device
VIP	I-Device
.	O
</s>
<s>
In	O
August	O
2006	O
,	O
Nuts	O
and	O
Volts	O
magazine	O
,	O
along	O
with	O
,	O
released	O
a	O
project	O
to	O
build	O
the	O
"	O
Cosmac	B-Device
Elf	I-Device
2000	O
,	O
"	O
based	O
on	O
the	O
original	O
Elf	O
,	O
with	O
some	O
newer	O
and	O
easier	O
to	O
find	O
components	O
and	O
enhanced	O
features	O
,	O
modules	O
,	O
and	O
functionality	O
,	O
including	O
the	O
STG1861	O
Pixie	O
Graphics	O
Replacement	O
board	O
that	O
is	O
functionally	O
equivalent	O
to	O
the	O
now-rare	O
RCA	O
CDP1861	O
integrated	O
circuit	O
.	O
</s>
<s>
A	O
series	O
of	O
newsletters	O
and	O
small	O
booklets	O
offered	O
by	O
Netronics	O
and	O
Quest	O
contained	O
1802	O
machine	O
language	O
and	O
CHIP-8	B-Device
programs	O
,	O
along	O
with	O
schematics	O
for	O
expanding	O
the	O
Elf	O
and	O
adding	O
peripherals	O
,	O
including	O
a	O
light	O
pen	O
.	O
</s>
<s>
Mike	O
Riley	O
has	O
written	O
an	O
editor	O
,	O
assembler	O
,	O
BASIC	O
and	O
FORTH	O
interpreters	O
,	O
a	O
BIOS	B-Operating_System
,	O
and	O
the	O
Elf/OS	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
that	O
will	O
run	O
on	O
expanded	O
Elf	O
systems	O
,	O
including	O
the	O
COSMAC	B-Device
Elf	I-Device
2000	O
.	O
</s>
<s>
Other	O
languages	O
available	O
are	O
noted	O
at	O
the	O
RCA	B-General_Concept
1802	I-General_Concept
Wikipedia	O
entry	O
,	O
including	O
interpreters	O
,	O
compilers	O
and	O
assemblers	O
.	O
</s>
<s>
Game	O
cartridges	O
for	O
the	O
RCA	O
Studio	O
II	O
contain	O
Chip-8	B-Device
games	O
,	O
which	O
can	O
run	O
on	O
other	O
1802	O
systems	O
.	O
</s>
