Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!tut.cis.ohio-state.edu!VAX1.CC.UAKRON.EDU!neoucom.edu!wtm From: wtm@uhura.neoucom.EDU (Bill Mayhew) Newsgroups: sci.electronics Subject: Re: IBM Keyboard Output Message-ID: <1991Feb18.185444.7021@uhura.neoucom.EDU> Date: 18 Feb 91 18:54:44 GMT References: <1991Feb17.065421.27814@athena.cs.uga.edu> Distribution: sci Organization: Northeastern Ohio Universities College of Medicine Lines: 38 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)