Path: utzoo!attcan!telly!problem!compus!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!cs.utexas.edu!uunet!world!jon_sree From: jon_sree@world.std.com (Jon Sreekanth) Newsgroups: sci.electronics Subject: Re: IBM Keyboard Output Message-ID: Date: 19 Feb 91 14:47:09 GMT References: <1991Feb17.065421.27814@athena.cs.uga.edu> <1991Feb18.185444.7021@uhura.neoucom.EDU> Sender: jon_sree@world.std.com (Jon Sreekanth) Distribution: sci Organization: The World Lines: 30 In-Reply-To: wtm@uhura.neoucom.EDU's message of 18 Feb 91 18:54:44 GMT In article <1991Feb18.185444.7021@uhura.neoucom.EDU> wtm@uhura.neoucom.EDU (Bill Mayhew) writes: 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. 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. Progress is wonderful :-) Seems like newer machines have dedicated keyboard controllers, then. I have schematics of IBM's original XT. The 'keyboard controller' on the mother board consists of glue chips. Roughly, there's a 9 bit shift register, and when the 9th bit gets a '1', it freezes clocking to the shift register, and interrupts the CPU. The CPU reads the byte using PA0-7 of the 8255 peripheral controller, then resets the chain, using yet another bit of 8255, so that the next character can be received. Note that the keyboard itself has a microcontroller, in IBM's case an 8048. / Jon Sreekanth Assabet Valley Microsystems Fax and PC products 346 Lincoln St #722, Marlboro, MA 01752 508-562-0722 jon_sree@world.std.com Brought to you by Super Global Mega Corp .com