Re: Cherry keyboards
- --- In email@example.com, Richard Cini <rich.cini@...> wrote:
>Don't guess - ANALYZE.
> All --
> I was poking around my shop today and came across a Cherry keyboard that I
> think was for a Steve Ciarcia computer, but I can't find any data on it.
> The interface connector
> is a SIP 1x16 with pin 2 missing. The main chip is an NEC micro controller
> (8048 I think). I'm guessing it's a parallel keyboard with certain keys
> directly connected to the interface (like the mu keys).
Use your ohmmeter and trace back from the pins on that connector to whatever chips they are connected to. Draw a partial schematic backwards from the connector. (Not the whole board!)
It's likely you'll find a TTL chip that's a 4-bit or 8-bit latch; or to some TTL drivers which in turn go to a latch (or maybe the 8048). It's likely you'll find a pin or two to some driver output - that may be the "strobe", or those extra keys. And you'll find power and ground. And there will be other outputs, maybe some inputs. A TTL guide will tell you what's inputs and outputs. I doubt the 8048 connects directly to that connector, but you'll find out.
Once you know power, ground and most of the outputs, then you can power up the keyboard and observe its operation with an oscilloscope. Outputs will be either high or low unless they are open collector; inputs will "float" at a few volts.
All a schematic would tell you after that, is what you already know, what you already stated. I'll bet you can do this in an hour.