17 Apr
2001
17 Apr
'01
9:11 p.m.
ok...i got my CDP-1802s so that i can build the COSMAC Elf...
now i just need the RAM that the schematics have....i believe that it is 2
256x4 RAM chips...if anyone has these or can let me know where i can find
them could you please let me know
thanks,
Robert Cobbins
17 Apr
17 Apr
10:51 p.m.
Try www.stocknsource.com. The Mototola MCM145101 is a 256 x 4 static RAM
that they have an ample supply of. I have the data sheets for it if you need
them.
18 Apr
18 Apr
4:03 a.m.
----- Original Message -----
From: <Demon02554(a)aol.com>
To: <classiccmp(a)classiccmp.org>
Sent: Tuesday, April 17, 2001 6:11 PM
Subject: looking for some old RAM chips
ok...i got my CDP-1802s so that i can build the COSMAC
Elf...
now i just need the RAM that the schematics have....i believe that it is 2
256x4 RAM chips...if anyone has these or can let me know where i can find
them could you please let me know
thanks,
Robert Cobbins
Are you going for an authentic recreation, or
would a functional substitution be adequate?
Given how expensive and scarce 1Kx4 2114s
are, 256x4s ought to be even moreso.
There are inexpensive 8-bit wide SRAMs
available with anything from 2Kx8 to
128Kx8, which will do the job nicely in 1 chip.
One tricky thing is that the 1802 multiplexes
its address output in 2 x 8 bit parts,
if I read the data sheet correctly. This means
you would connect only A0...A7 of the available
address pins from the SRAM to the 1802 and
ground the remaining address inputs. You'll
"waste" all but 256 bytes but then again, memory
is cheap. At least the silicon kind. :)
You can demux/latch too, if you really want to
toggle in more than 256 bytes! =:-O Aiiiiieeee!!!
11:04 a.m.
--- Demon02554(a)aol.com wrote:
ok...i got my CDP-1802s so that i can build the COSMAC
Elf...
now i just need the RAM that the schematics have....i believe that it is 2
256x4 RAM chips...if anyone has these or can let me know where i can find
them could you please let me know
I've seen places with the 1822s for sale in the past couple of years. It's
not the same, but B.G. Micro has 2102s for <$1 each (the web page from their
online catalog is at http://www.bgmicro.com/pdf/page5.pdf)
You could always use a more modern 2016 or 6264 or such and just tie the
upper address lines to 0. You can scavenge those from old Ethernet cards
and the like. The speed requirements of the 1802 are not harsh. I think
you can get away with 450ns RAM on a 1Mhz design.
-ethan
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2:33 p.m.
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7:34 p.m.
There are some NMOS versions of the 5101, i.e.2101 that are pin-compatible,
though they want to be operated at 5 volts, that might do so long as you're not
going to run it from a solar cell or a single AAA battery. These occasionally
pop up at Jameco, JDR, etc.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Wednesday, April 18, 2001 12:33 PM
Subject: Re: looking for some old RAM chips
ok...i got my CDP-1802s so that i can build the COSMAC Elf...
now i just need the RAM that the schematics have....i believe that it is 2
256x4 RAM chips...if anyone has these or can let me know where i can find
them could you please let me know
If you're not trying to build an exact replica, but just something that
will work, you could use a more modern SRAM, like a 6264 (8K*8). Such
chips are cheap now. Just tie the unused high-order address lines on the
RAM to ground, leaving 8 low-order ones to connect to the system address
bus. The rest of the circuitry should be essentially unchanged.
I've done this sort of thing several times when repairing older equipment.
-tony
19 Apr
19 Apr
2:32 a.m.
Check your supply and signal voltages and cut traces/reroute power or
things might be interesting.
Regards,
Jeff
In <002b01c0c860$162ae760$9cc762d8(a)idcomm.com>om>, on 04/19/01
at 02:32 AM, "Richard Erlacher" <edick(a)idcomm.com> said:
> If you're not trying to build an exact
replica, but just something that
> will work, you could use a more modern SRAM, like a 6264 (8K*8). Such
> chips are cheap now. Just tie the unused high-order address lines on the
> RAM to ground, leaving 8 low-order ones to connect to the system address
> bus. The rest of the circuitry should be essentially unchanged.
--
-----------------------------------------------------------
Jeffrey S. Worley
President
Complete Computer Services, Inc.
30 Greenwood Rd.
Asheville, NC 28803
828-277-5959
Visit our website at HTTP://www.Real-Techs.com
THETechnoid(a)home.com
-----------------------------------------------------------
9:37 a.m.
--- THETechnoid(a)home.com wrote:
Check your supply and signal voltages and cut
traces/reroute power or
things might be interesting.
Regards,
Jeff
In <002b01c0c860$162ae760$9cc762d8(a)idcomm.com>om>, on 04/19/01
at 02:32 AM, "Richard Erlacher" <edick(a)idcomm.com> said:
>> If you're not trying to build an exact replica, but just something that
>> will work, you could use a more modern SRAM, like a 6264 (8K*8)...
In the case of the 1802, that's not an issue. The "original" SRAM for
the Elf is a pair of 1822s - CMOS, single supply voltage (unlike early
EPROMS (1702) and DRAMS (4116 and earlier). Due to the fact that most
hobbyist 1802 designs had some TTL (like the cool TIL311 displays in
the original P-E article and on the Quest Elf), they were run with a
regulated +5VDC supply. A 2016 or 6264 or similar SRAM will work just
fine as is; add a latch for the upper address bits to use it all.
-ethan
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