Thanks! Every answer has been very useful! I spent days trying to figure
out what went wrong. I rebuilt and rewired the entire input and output
section, tested every IC on a separate breadboard, check voltages with
multimeter on vcc and ground pins, measured signal with an oscilloscope and
it still doesn't work. These are the symptoms:
- the 4016 work when the ENABLE pins are high (tied to a voltage source)
yet they don't let anything go through when wired to the control circuit
- the HP hex displays work perfectly except the control circuit never sends
logic low signal. When the LATCH ENABLE pin is low, the display shows
whatever comes from the bus. When wired to the ground, the display happily
updates its content when I poke random bus wires. I tested the hex displays
(four actually) separately, they work fine.
Therefor the trouble is somewhere in the control circuit. The 4013 and the
4023 seem to be the culprits.
On 5 March 2012 21:48, Ethan Dicks <ethan.dicks at gmail.com> wrote:
On Mon, Mar 5, 2012 at 4:15 PM, allison <ajp166 at
verizon.net> wrote:
> Ethan Dicks wrote about the COSMAC Elf:
> It's certainly true that the 4016 and 4066 have differences in their
> characteristics. However, in the simple way in which it is used in the
Elf,
I
can't see how it would make any difference. I can't say that I've
actually tried it, though.
I have no difference.
I was told by the engineer who made the Quest SuperElf that he had a
problem subbing 4066s for 4016s. He was rather insistent there was a
problem. I have not tried it myself, either. My breadboard Elf and
my Quest Elf have 4016 switches.
that and also making sure all the wires go where
they are supposed to.
Indeed. That was my problem on my Popular Electronics Elf.
I've built many of the COSMAC ELFs over the
years and still have my wire
wrapped original, a
QUEST PCB version and a few more wire wrapped variants. I made a version
of
the ELF on S100.
Nice.
I also have the EELF and ELF2000. It was a
simple and very non-critical
CPU to build up and make work.
Yep. I've built those, too. I just pulled out my Elf2K this weekend.
I need to re-do the switch plate label - somehow a drop of oil got
onto the paper and left a stain.
Of all the 1802 is the most interesting as
it's
not unlike the PDP-8 in that its
simple to the extreme yet still useful.
Agreed.
There's one thing I can do on my Elf2000 that I still can't do on a
PDP-8... play Zork.
-ethan