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AT2XT keyboard converter

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    AT2XT keyboard converter

    The AT2XT keyboard converter (AT2XTKB) project is a Vintage Computer forum driven project to develop and manufacturer a keyboard adapter which allows users to attach AT keyboards to XT class computers. This, for example, allows XT machines to be used on KVM (keyboard/Video/Mouse) switches.

    The project is entirely open source, from the design, schematic, layout, bill of materials, and firmware.




    This page will provide links to all the resources utilized in the project.
    You can discuss this project here

    The PIC Chip

    The heart of the circuitry is a PIC12F629 integrated circuit, referred to as "PIC chip" in other sections of this page.

    From the factory, the EEPROM component within the PIC12F629 contains no firmware and therefore needs to be programmed. An EPROM programmer is required to write firmware into the PIC12F629. The custom firmware created for the PIC12F629 in the AT2XTKB is available via a link below, in the 'Downloads' section.

    Scancode E0 Pass-Through

    In August 2010, it was identified that certain non-US scenarios need to have the E0 scancode passed straight through the AT2XTKB. The VCF discussion on this starts [here].

    After investigation on how to implement that, it was discovered that the AT2XTKB would need to be able to work in one of two modes:
    1. Do not pass-through scancode E0; or
    2. Pass-through scancode E0.

    It was decided to modify the PIC chip's firmware (became version 0.93) and use the then unused jumper, JP1, to select the mode of operation. At that time, the design flaw in regard to jumper JP1 was detected (see 'Jumper JP1' section below).

    If you are in the rare situation of needing 'scancode 0xE0 pass-through' functionality on your AT2XTKB, you will need to:
    1. Per the 'Jumper JP1' section below, modify your AT2XTKB to cater for the JP1 flaw; then
    2. Per the 'Jumper JP1' section below, set jumper JP1 as required.

    Jumper JP1

    At the design time of the AT2XTKB, jumper JP1 was not used, included for possible future use.
    Later, when the PIC code was being changed to cater for 'scancode E0 pass-through' functionality, it was discovered that there was a design flaw in the AT2XTKB that prevented proper jumper use.
    The flaw does not affect the vast majority of AT2XTKB users - the AT2XTKB works as expected - there is no need to address the flaw.
    For those who need 'scancode E0 pass-through' functionality, the flaw needs to be fixed by adding a pullup resistor, R3, of a value of 47K ohms (actually, anything between 2K and 100K ohms) between pin 1 (Vcc) and pin 4 of the PIC chip.

    Jumper settings:

    Pullup R3 not present and JP1 on: Normal operation
    Pullup R3 not present and JP1 off: Normal operation

    Pullup R3 present and JP1 on: Normal operation
    Pullup R3 present and JP1 off: Scancode E0 passed through

    Downloads

    Firmware for PIC Chip (PIC12F629)

    Firmware - version 0.94 - Source code
    Firmware - version 0.94 - HEX file (What your EPROM programmer uses.)(Click here for info about the OSCCAL value.)
    PCB/Schematic

    Schematic view #1
    Schematic view #2 (Resistor R3 not shown.) (Due to a limitation in the drawing software, the arrangement of pins on large DIN connectors is wrong.)
    Schematic view #3 (Resistor R3 not shown.)
    Schematic as an Eagle file
    PCB board layout (Seems slightly out of date-there are now mounting holes in the corners.)(Holes for large DIN connectors facing wrong way.)
    XTATKEY_094.zip
    Bill of Materials

    Parts sourced from Digikey Electronics
    Code:
    Qty  Digikey #              Item     
    1                        AT2XT Keyboard PCB (get this from andrew lynch) or breadboard your own
    2    CP-2350-ND          CONN DIN 5 PIN FEMALE PCB 
    1    CP-2260-ND             CONN MINI-DIN 6 PIN FEMALE PCB (yes, 6 pin.  do not get 5 pin PS/2 connectors!)
    1    PIC12F629-I/P-ND    IC MCU CMOS FLASH-BASE 8BIT 8DIP
    1    A24807-ND           CONN IC SOCKET 8POS DIP TIN
    1    568-1360-1-ND       DIODE SW HS 100V 200MA DO-35
    2    P4.7KBACT-ND        RES 4.7K OHM CARBON FILM 1/4W 5%
    1    P10375TB-ND         CAP 47UF 25V ELECT M RADIAL
    1    A30916-ND           CONN HEADER VERT 2POS .100 TIN (there's a million of these types of headers - not actually req'd)
    1    ?                   47K ohm resistor (R3) between pin 4 and Vcc. (only needed for jumper to select different operation for non-USA keyboards)
    [wiki]Category:Hardware[/wiki]
    Last edited by mbbrutman; July 20, 2019, 12:17 PM. Reason: Fix broken forum links
    The Vintage Computer and Gaming Marketplace
    The Vintage Computer

    #2
    Just for your reference, I have attached the files to another classic computing forum as there is some interest by some users to have this adapter and produce a small series of them. See http://forum.classic-computing.de/in...4253#post94253
    <album>

    Comment


      #3
      Is it posible to build this keyboard converter to connect an XT keyboard to an AT computer?

      Comment


        #4
        Originally posted by mac512 View Post
        Is it posible to build this keyboard converter to connect an XT keyboard to an AT computer?
        Why would you want to do that?

        XT keyboards generally suck in comparison to AT keyboards and AT keyboards are really plentiful.

        Do you happen to have an exceptional XT keyboard that outperforms the AT keyboards in some magnificent manner?
        PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

        Comment


          #5
          For a long time I've been thinking of replacing my 5155's motherboard with a 286/386 board but I haven't been able to figure out a way to connect the original keyboard...

          Comment


            #6
            Originally posted by mac512 View Post
            For a long time I've been thinking of replacing my 5155's motherboard with a 286/386 board but I haven't been able to figure out a way to connect the original keyboard...
            I get exactly what you're saying Mac, did you figure out how to connect to your keyboard yet?

            Comment


              #7
              Originally posted by mac512 View Post
              Is it posible to build this keyboard converter to connect an XT keyboard to an AT computer?
              This guy:
              http://www.kbdbabel.org/

              Has done several strange keyboards to AT converters, including PC/XT. I agree with @Stone it's not the most useful of directions to my mind, but it has been done. If anything the simpler protocols are easier to read than AT, making such conversion actually simpler to implement than the other direction.

              It's one of the sources I've been using for information -- and what led me to question the PC/XT timing info I was seeing as the math on his charts:

              http://www.kbdbabel.org/signaling/index.html

              ... don't seem to add up right, and are inconsistent with how most clocked protocols have a delay to compensate for rise/fall time.
              From time to time the accessibility of a website must be refreshed with the blood of owners and designers. It is its natural manure.
              CUTCODEDOWN.COM

              Comment


                #8
                Originally posted by Stone View Post
                XT keyboards generally suck in comparison to AT keyboards and AT keyboards are really plentiful.
                Regarding the AT2XT keyboard PCB: Who is Andrew Lynch and how do I get in touch with him? I recently acquired another 5160 (chassis / cpu only) and want to use an AT keyboard with it.

                -CH-

                Comment


                  #9
                  This is he:

                  http://www.vcfed.org/forum/member.php?3051-lynchaj
                  PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

                  Comment


                    #10
                    Hi

                    Is there a Gerber File available for the AT2XT board?

                    Regards
                    Thomas

                    Comment


                      #11
                      Originally posted by gastrodus View Post
                      Hi

                      Is there a Gerber File available for the AT2XT board?

                      Regards
                      Thomas
                      I've been looking for a while, hopefully someone knows where they are...

                      - Gary

                      Comment


                        #12
                        I'm not n expert on the subject but I thought you could generate Gerbers from within Eagle: https://learn.sparkfun.com/tutorials...rating-gerbers

                        -CH-

                        Comment


                          #13
                          I uploaded the KiCAD file sets, new schematic and PCB layout, and the Gerbers on retrobrewcomputers.org forum

                          Comment


                            #14
                            Hi.

                            I designed a 3D printed custom case for the AT2XT keyboard converter.

                            Available here: https://www.thingiverse.com/thing:2406022

                            Enjoy!!

                            Comment


                              #15
                              Cute case, printed up nicely.

                              Thanks for making this available.

                              - Gary

                              Originally posted by Rodolfo View Post
                              Hi.

                              I designed a 3D printed custom case for the AT2XT keyboard converter.

                              Available here: https://www.thingiverse.com/thing:2406022

                              Enjoy!!

                              Comment

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