Intersil EPROM

Ethan Dicks ethan.dicks at gmail.com
Tue Jun 16 10:51:09 CDT 2009


On Tue, Jun 16, 2009 at 10:29 AM, Philip
Pemberton<classiccmp at philpem.me.uk> wrote:
> Ethan Dicks wrote:
>>
>> I have one 1802D in a ceramic package.  ISTR it will push to 10V
>> (which is required to take it much above 1MHz).
>
> It's been a while since I powered it up, but I've got a COSMAC Elf
> somewhere. CDP1802 CPU, CDP1864 "Pixie" graphics chip, 256 bytes of RAM, and
> a core clock of 1.789773MHz (3.579545MHz divided by 2). The whole board is
> running on 5V, and works fine.

There are newer versions of the 1802 that work fine at NTSC
colorburst/2, but back in the late 1970s, ISTR the inexpensive CPUs
would only work at like 3V-6V and definitely would not work at
3.57...MHz (I know because I tried using just a colorburst crystal and
it didn't go), but OTOH, one of the variants (D? E?) was the fastest
available, if you pushed it to +10VDC Vcc.

Now, I have plenty of 1802 gear running at 1.789MHz and running fine,
but with recently made (1990s) CPU chips.

> I don't think I ever did anything remotely interesting with it, but it's
> still a neat toy.

It's a great toy.  I still have my design/programming notebooks from
when I was 11-12 years old, learning assembler on a friend's Elf.  His
was the Quest Elf board (my first one was, too), but with the TIL311s
and the switches offboard, via a 24-pin cable.  My Elf (which appears
on the Yahoo Groups photo page for 'cosmacelf') is in a 2-piece Radio
Shack metal project box, with a compatible connector wired in - I used
to use my CPU with his external front panel, and I've never rewired my
board for local control.  The soldering is bad enough (I was just a
kid) that I've long contemplated removing all the parts and the crappy
sockets and starting fresh (and installing local switches since I no
longer have the external front panel).  Of course I could just make an
external front panel - I did just find some nice C&K paddle switches
from some discarded Vaisala gear which will be *perfect* for an Elf...

Mostly for me, the 1802 was a learning bed - a place to hack stuff at
the gate level and to program in machine code in an environment I
could single-step through things.  I'm happy to have built a
"full-blown" Elf2000 and to have helped debug the Z-machine for ElfOS,
but that first Quest Elf, way back, was instrumental in learning to
understand how microprocessors work.

Besides simple counting programs and switch-flipping programs, I never
really did much with the 256-byte Elf, but it was still a great
machine.

-ethan



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