20 Sep
2013
20 Sep
'13
1:19 p.m.
I wrote down a key "replacement" table, and
from what I see these AAE
encoders are generating codes exactly like they was AAD version...
As I am sure you are ware, the 'AAE' specifies the programmign of an
internal ROM which generates the output code from the key matrix
positions. So as yo've found, if you fit one with the wrong programming,
it works, but gvies the worng keycodes.
Maybe here there's a problem of wrong markings
over the ICs?
Anybody ever heard of similar issues, or bought these encoders from
Littlediode and had similar problems?
Not with this IC, but there are plenty of fake and mislabelled
semiconductors around.
2 stories, one from a fried, one that happened to me.
A friend found a supplier (in CHina, I thin) who had a vast list of
ICs they claimed ot be able to source, including a number of HP custom
parts. He asked about oen of the latter (I think a ROM for the HP41
calculator) and was asked 'what package and how many pins'. Given that
said IC ony ever existed as an 8 pin DIP it is clear that said company
would lable any package with any number.
The one that happened ot me. A couple of weeks ago I bought what were
claimed ot be 1A SCRs (thyristors, whatever). I fitted on into the
cirucit I wwas working on and found it was 'on' all the tiem. Even with
no input to the gate, the gate and cathode being linked by a resistor, it
was still turnign on at switch-on. And it did not test shorted
out-of-circuit.
After much testing, I found I had, in fact, been supplied with PNP
transistors (!). One had the correct number for the SCR on the can, the
other 2 I had were not labeleld at all. If you think about the circuit,
it turns out that the thing ends up with emitter and collector swapped
round and a resistor between base and what is nwo the collector (most -ve
electrode). OK, it's a poor transistor with minimal current gain but
that reissotr supplied enough current to bias it on.
So yes, mislabelled components are alas all too common now.
I suspect that they came from a production lot
wrongly-marked.
You were lucky, I think, you got a keyboard encocder and not just some
other 40 pin device.
If I was being unkind I would guess that soembody had noticed the AAE
version was useful for fixing Apple ][s, the AAD version was not a lot of
use, and so they got re-labelled. They may not even be National
Semiconductors devices..
-tony