PC Hardware Input/Output Port: Keyboard

The keyboard scan codes you see listed in Books and FAQs and so forth are NOT current for a MFII (101-key expanded) keyboard. The Linux source code does document all this.

Typical data transfer speed from the keyboard  is approx. 8kHz . The clock pulses are 60 or 70 uS long so 120uS for the period. The clock rate can differ significantly between  PCs

Many keyboards have automatic XT/AT mode detection. This worked in several different ways. e.g. one keyboard would send a code with a deliberate parity error, and if the host didn't request a re-send it went into XT mode.

Topics:

• Interfacing to people
• Interfacing to Keyswitches (Keyboard decoding)
• Debouncing, Switches
• Keyboards with PICs
  • Jinx PC Keyboard Capture and Emulation using a PIC 18F1320 includes detailed info on PC keyboard signals and timing.
• Keyboards with Ubicom SXs
• DIN connector gotcha
• Interfacing to Rotary Switches
• 1 wire LED and switch

Michael Hetherington's USB Keyboard demo

Caller ID Keyboard wedge: ddj article and source code

See also:

• https://hackaday.com/2021/08/30/chordie-chording-keyboard-speaks-no-qwerty/ 3D printed case and individual switches, but the trackball is the best.+
• https://www.ixqprint.com/ Huaisong Industrial is the one of the membrane keypad manufacturer in china.+
• https://www.dofrp.com/ Best FRP manufacturer--DOFRP.+
• http://www.instructables.com/id/Chording-Keyboard-BLE-and-USB/?ALLSTEPS BLE chording keyboard with 3D printed case.+
• http://chordite.com/ Yet Another One-hand Keyboard.
• http://chorder.cs.vassar.edu/spiffchorder%3Aforside SpiffChorder is an open source, atmel based, USB or bluetooth chording keyboard.+
• http://www.keyglove.net/ Open source chording keyboard and air mouse built into a glove.+
• http://www.ibizpda.com/ iBIZ Virtual Keyboard is a laser projection of a keyboard on any surface with positional feedback on your fingers to simulate typing. The only concern is the lack of "feel". It will be like a "chicklett" keyboard, but worse.
• http://pannam.com/ Pannam has a Free Membrane Switch Design Guide+
• http://www.arne.si/~mauricio/Kbdfaq.htm PC Keyboard FAQ Awesome! (cached 20010201151637)
• http://www.tegic.com/ using a 10 key pad to enter text
• http://web.mountain.net/~roair/wearjunk.html wearable chording keyboard.
• Articles about XT and AT type keyboards can be found in April/May 1995 issues of Circuit Cellar Ink.
• An early copy of Micro Cornucopia ( March-April 1990 ) has the details about standards, interface chips etc
• John Voth has keyboard interfacing information at: http://nyquist.ee.ualberta.ca/~jdv/
• http://www.enterprise.ca/~jbilous/kybrd03.htm
• http://www.barcodeman.com/scan_doc.html
• http://www.senet.com.au/~cpeacock for details on how to interface an AT keyboard to a system expecting ascii input.
• A PC Keyboard FAQ has been written by Mark Schultz. Send e-mail to mchultz@wctc.net for details.
• Go to the Aminet site (eg. ftp.netnet.net) and go to hard/hack, there you'll find 2 or more files for PC keyboard interfaces to Amiga. There is some documentation for the AT keyboard protocol.
• Check out the Philips site. There is supposed to be an app note for PC keyboard to serial format.
• http://www.repairfaq.org/filipg/LINK/PORTS/F_Keyboard_FAQ.html
• http://members.tripod.com/~ilkerf/c64tower/F_Keyboard_FAQ.html is Yet Another Keyboard FAQ.
• http://www.brouhaha.com/~eric/pic/
• http://www-dept.cs.ucl.ac.uk/staff/B.Rosenberg/kbd/chord.html Interesting Chord Keyboards summary:
• http://www.atmel.com/atmel/acrobat/doc1235.pdf has C code for interfacing an AVR processor to a keyboard.
• http://www.hut.fi/Misc/Electronics/hwprojects.html#pc_keyboard, good PC hardware projects
• Hagstrom Electronics, 2 Green Lantern Boulevard Endicott, New York 13760, 1-888-690-9080 9x9 and 12x12 matrix to PC or RS232 encoder boards
• http://www.usar.com/prodnser/keycod.htm
• http://junitec.ist.utl.pt/einfo/hwprojects.html#pc_keyboard
• http://www.freebsd.org/~fsmp/HomeAuto/Focus.html
• Ken's Gameboy and PIC Projects Page
• http://panda.cs.ndsu.nodak.edu/~achapwes/PICmicro/keyboard/keyboard.html
• http://www.piher-nacesa.com/paginas/product.htm
• http://web.mit.edu/invent/www/inventorsI-Q/levypg.html to push 1 you actually depress 1QWAS. Q is QA1W. Shown just about actual size. Why didn't I think of that? Invented by David Levy of TH, Inc. ("think" get it?), called "OneTouch" or "Fastap" marketed by digitwireless and now available from Telus in Canada

• http://32.97.166.75/imouse/
• http://www.ednmag.com/ednmag/reg/2000/02032000/designideas.htm "Keyboard data-acquisition system is cheap and simple"
• http://www.mikerj.clara.net/keypad.html

See also:

• http://www.al-williams.com/pak6.htm For a hardware solution (read PS/2 keyboard or mouse to RS232)+

Archive:

• PICList post "IR as a substitute for tact switch" +

Uche Nwoko of Multi-Electronics Design Says:

A simple experiment for those looking for, a common keyboard that is capable of encoding 9 key strokes into four binary bit. what I did was to use an IC 74HC147, known as 10 to 4 line priority encoder, as a keyboard to controle a wireless remote system, with this IC I can be able to achive an Output of 4 binary code from 0 to 9, whereby i interface the binary output with any encoder to give me the right data i needed to controle my design.
To construct a keboard from 74Hc147 all 1 to 9 input pins should pull high with 10k resistors, then each of the input is connected to micro push buttons,with this buttons i can be able to sellect any of the input from 1 to 9, if all of the 9 iputs are on high position, the output will be Automatically 0 (Zero), i.e if the output is invert, that is why I did not have 0 button on my keboard, with the help of cd4511 you can be able to read out the output from 7 segment display.
Below is the input and Output Table.

A B C D 1 2 3 4 5 6 7 8 9
1 1 1 1 = 1 1 1 1 1 1 1 1 1 when output invert = 0, if not invert = F
0 1 1 0 = 1 1 1 1 1 1 1 1 0 when output invert = 9, if not invert = 6
1 1 1 0 = 1 1 1 1 1 1 1 0 1 when output invert = 8, if not invert = 7
0 0 0 1 = 1 1 1 1 1 1 0 1 1 when output invert = 7, if not invert = 8
1 0 0 1 = 1 1 1 1 1 0 1 1 1 when output invert = 6, if not invert = 9
0 1 0 1 = 1 1 1 1 0 1 1 1 1 when output invert = 5, if not invert = A
1 1 0 1 = 1 1 1 0 1 1 1 1 1 when output invert = 4, if not invert = B
0 0 1 1 = 1 1 0 1 1 1 1 1 1 when output invert = 3, if not invert = C
1 0 1 1 = 1 0 1 1 1 1 1 1 1 when output invert = 2, if not invert = D
0 1 1 1 = 0 1 1 1 1 1 1 1 1 when output invert = 1, if not invert = E

The above table is exctly how the input and out out look like, if necessary the output can be invert with the help of Ic CD4069 or CD4049, I wish any reader a success, if you want to try this simple design.

Questions:

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