On Fri, Mar 2, 2012 at 9:08 PM, Gergely L?rincz <alkopop79 at gmail.com> wrote:
I wonder if anyone has experience with Cosmac Elf.
I've been trying to
build one on breadboard but have troubles with the input section. Please
let me know if you have built one! Thanks
I built one from the original Popular Electronics magazine plans
(including the CDP1861 interface). What's the problem?
In my own case, when I first built it, I had a wiring fault that
caused odd input behavior. I simply miscounted pins and miswired D5
or D6 somewhere. The fix was to move the join.
To guess, I know of one common issue with hand-made 1802 designs - the
4016 and 4066 are not 100% interchangable. They have different switch
response characteristics. ISTR the older designs used 4016 switches
which are harder to find now than 4066 switches.
If not that, then the other issue to investigate is to ensure that the
input button is debounced and generating proper DMA-IN requests (and
that the CPU is in LOAD mode).
-ethan