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I overclocked my IBM 5150...

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    I overclocked my IBM 5150...

    I got the PC-Sprint schematics and designed a new pc-sprint board. Got the parts from jameco (they still have 8284a) and voila.... but my DRAM's are all 200ns! bummer, So the 22.1Mhz didn't work, I got a all sorts of parity error. So I got the highest oscillator here 17.43 and it worked I will buy other frequencies until I find the limit for my machine...

    Pics
    pc-sprint1.jpg

    pcsprint2.jpg

    pcsprint3.jpg

    pcsprint4.jpg

    here the KiCad files for whomever wants it:

    https://sites.google.com/site/tandyc...edirects=0&d=1

    #2
    Can you successfully use cassettes with the overclocked 5150? I am serious. I remember the question of CPU speed versus the cassette interface coming up a few times in the past so this might be the best chance to prove things.

    Comment


      #3
      Oh please don't make me do it Luckly I don't have the cable and I hope it's not the same for the TRS-80 Color...

      Comment


        #4
        Originally posted by Retro Canada View Post
        Oh please don't make me do it Luckly I don't have the cable and I hope it's not the same for the TRS-80 Color...
        Oh boy looks like it does .... ok one day when I am bored to death I will get my cassette and try it.... hope this day never comes

        Comment


          #5
          Good evening,
          Have you made any progress in overclocking your 5150? I would like to try to do in my ...

          Comment


            #6
            I'd also be interested in one of these. I have no experience in getting PCBs manufactured - if I send the KiCAD files off to a PCB fab service will they know what to do with them? Alternatively is anyone selling these boards? Happy to source the components and solder one up.

            Comment


              #7
              Originally posted by Retro Canada View Post
              I got the PC-Sprint schematics and designed a new pc-sprint board. Got the parts from jameco (they still have 8284a) and voila.... but my DRAM's are all 200ns! bummer, So the 22.1Mhz didn't work, I got a all sorts of parity error. So I got the highest oscillator here 17.43 and it worked I will buy other frequencies until I find the limit for my machine...

              Pics
              [ATTACH=CONFIG]42113[/ATTACH]

              [ATTACH=CONFIG]42114[/ATTACH]

              [ATTACH=CONFIG]42115[/ATTACH]

              [ATTACH=CONFIG]42116[/ATTACH]

              here the KiCad files for whomever wants it:

              https://sites.google.com/site/tandyc...edirects=0&d=1
              Hey again. I'm really interested in trying out this upgrade so I sent your gerber files off to PCBWay to get some boards manufactured. Hopefully that's the reason you shared them! I really do appreciate the effort, I don't have the skills to do it myself and I seriously doubt they would've accepted the original ASCII art diagrams! Due to economies of scale I decided to go for 20 (also if I screw any up). I've also ordered enough components to build them.

              Once I've built and got one working in my 5150 I guess I'll be looking to sell the extras but I'd need your blessing to do that as you did the CAD drawings. Not looking to profit - I just think it would be good to make these available to the reto community as I have the parts anyway. I see you haven't been active on here for over a year so maybe you won't see this message but I thought it was worth a try.

              Will keep everyone updated with my progress!

              Comment


                #8
                Just curious, is it just the CPU or the whole system that's overclocked?

                I would imagine the benchmark readings could be affected if the 8253 was increased in speed as well.
                Current systems owned by me:
                Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
                Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

                Comment


                  #9
                  It had better be just the CPU with all of that--otherwise, an XCO feeding the EFI input (pin 14) and connecting pin 13 to an 8255 unused output would do it.

                  Comment


                    #10
                    This mod adds a separate timing crystal and 8284A oscillator chip specifically to clock the CPU. It would be possible to overclock the whole system by dropping a faster crystal straight into the motherboard but I hear this causes all sorts of timing issues leading to instability. I'm sure I'm probably preaching to the (more knowledgeable than me!) choir on that anyway.

                    I'm not sure of the effect on the 8253, I'll have to look into it a bit more. It would appear from my very rudimentary research that the 8253 is responsible for refreshing the DRAM? In which case I imagine there would be some benefit to clocking that at a higher rate as well - depending on the speed of the RAM of course.

                    [Scuttles off to look for 5150 motherboard schematics...]

                    Comment


                      #11
                      Why would clocking the refresh at a higher rate be beneficial? If you check some 1980s articles on 5150/60 speedup, there was code to reduce the refresh rate. The 5150 is supposed to aim for a 2 msec refresh, when in fact, a much lower rate is perfectly decent. Refresh on the 51x0 occupies about 10% of overhead.

                      Comment


                        #12
                        Originally posted by Chuck(G) View Post
                        Why would clocking the refresh at a higher rate be beneficial? If you check some 1980s articles on 5150/60 speedup, there was code to reduce the refresh rate. The 5150 is supposed to aim for a 2 msec refresh, when in fact, a much lower rate is perfectly decent. Refresh on the 51x0 occupies about 10% of overhead.
                        Fair enough, I'm still learning when it comes to this stuff. It seems that faster is not always better. I'll try to see if I can find some of the articles you mentioned. Yet another data point to add to my research, thanks!

                        Comment


                          #13
                          If you can't find any, I may have a copy of one in my files. However, the business of the refresh was used by a couple of (unscrupulous) outfits advertising a "speedup" for your PC. You may also find references to the trick on SIMTEL20.

                          Comment


                            #14
                            https://www.reenigne.org/blog/how-to...-dram-refresh/

                            So in an overclocked state the IBM 5150 would definitely not need to refresh every 72 cycles since more cycles would occur over a duration

                            Interesting

                            Comment


                              #15
                              Originally posted by rmay635703 View Post
                              So in an overclocked state the IBM 5150 would definitely not need to refresh every 72 cycles since more cycles would occur over a duration
                              A related diagram is at [here].

                              Comment

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