🚀 go-pugleaf

PC clone keyboards do not produce character encoded output.  What
you get is a make code when a button is depressed and a follow-up
break code when said key is released.  IBM keyboards are supposed
to be capable of n-key rollover, so fairly elaborate keeping track
of what is going on in the keyboard is necessary at the receiveing
end.

The recieving end is typically a dedicated 8741 or simialr
ROM-bearing microprocessor that decodes the keystrokes and presents
the keystrokes to the BIOS through an interrupt drivien routine.
Note that an IBM keyboard sort-of needs intelligent support from
the receiving end.  The keyboard itself is capable (in IBM's case)
of generating three differnet sets of scan code mappings that are
host-selectable.  Also each key is individually programable to be
make/break (like a letter key) or sticky (like caps lock) or
typematic (auto repeating).

A person considering using a low-cost PeeCee clone type keyboard in
a new product might want to see if there is a source of
preprogrammed keyboard controller proceessors around.  The keyboard
controller in clone machines is typically done by the same company
that writes the BIOS ROMs since the two systems have to work so
much in concert.  For instance, the BIOS in my '386 at home is
American Megatrends (AMI) and so is the sticker over the quartz
window on the keyboard controller (think in my case it is an 8741
uP).  It is left as an exercise for the reader to contact AMI to
find out what, if anything, is available.

PeeCee keyboards aren't as simple as they look at first blush!

==Bill==


-- 
Bill Mayhew      NEOUCOM Computer Services Department
Rootstown, OH  44272-9995  USA    phone: 216-325-2511
wtm@uhura.neoucom.edu   ....!uunet!aablue!neoucom!wtm
via internet: (140.220.001.001)