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Powertran Cortex

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    I replied to your previous message about the VDP and crystals the other day but now can't see my reply, strange.
    Yes, I'm sure changing it fixed the beeps but I think I changed it for a 74HC259 which was all I had at the time. So maybe it's a marginal timing issue.
    There are 2 on the board so i'll try swapping the 74HC259 with the other 74LS259.

    Jim

    Comment


      Originally posted by Stuart View Post
      No caps on the VDP crystal - just no video signal. Looking at the VDP oscillator inputs with a 'scope and the signal is all over the place. Did wonder if it's because I'm using one of the modern "1/4 height" crystals, but the crystal in the VDP data sheet would have been "full height" and the data sheet specifies the caps.


      I'm using a TMS9918 VDP to give a direct NTSC composite output (with a 560 Ohm resistor to ground). The picture is not great (in terms of clarity, but rock steady as far as sync is concerned), but is consistent with another project where I've used the 9918. See the screenshot at <www.avjd51.dsl.pipex.com/cortex_screen.gif>. The vertical banding looks about the same as the horizontal resolution. I've tried adding a simple transistor buffer stage to the output but it made no difference. Some sort of filtering to smooth the blue background would also smooth the pixels you're trying to see?

      Now lets compare that with the TI-99/4A which gives a far better picture. There's a circuit diagram of the TI-99 here, with the video circuit on page 60 of the PDF: <www.avjd51.dsl.pipex.com/ti/console_circuit_diagram.pdf>. I've tried the filter circuit on the video output on one of my other systems and that didn't make any difference either. The VDP crystal circuit is not the simple crystal and cap circuit in the data sheet - why the effort for this particular circuit?

      Does anyone have any 'analogue contacts' who might be able to shed some light?

      Stuart.

      Lets try this reply again.

      The crystals in mine are the originals from the kit.
      The TI-99 circuit is interesting, it has a fair bit of filtering on it's power supply, maybe this could be the cause of the banding you are seeing on the display.
      I don't notice it on mine but probably the picture isn't good enough.
      I did try the direct power connections to the VDP as recommend in one of the newsletters but it didn't make any noticeable difference (so far).

      The TI-99 crystal circuit is certainly the most complex circuit I've seen for an oscillator but I wouldn't like to guess as what the extra part are supposed to be doing, I'm not that good on analog electronics, more digital and software me.

      Jim

      Comment


        A little more info on the video side of things ...

        Turns out I didn't have any bad VRAM chips after all. The problem was that the 9918 was generating so much noise (~200mV) that it was interfering with its operation or the operation of the RAM. I've removed the decoupling cap from the VRAM chip nearest the 9918 and replaced it with a 470uF cap which has completely cured it. Added a 0.1uF decoupling cap under the 9918 for good measure.

        I've also tried one of my favourite pastimes - trying random caps across the video output. Which unusually has been very productive. A 4700pF cap has changed this ...

        <www.avjd51.dsl.pipex.com/cortex_screen.gif>

        ... to this ...

        <www.avjd51.dsl.pipex.com/cortex_screen_2.gif>

        ... and this ...

        <www.avjd51.dsl.pipex.com/cortex_screen_3.gif>.

        Might change the default foreground colour to black as it is alot clearer.

        Stuart.

        Comment


          A beautiful picture. Well done!
          Torfinn

          Comment


            Hello to you all, I also have a Cortex that I built in the 80's. It's a Mark 1.
            I must admit that it was quite a surprise to find an active group of enthusiasts who also have one of these.
            My Cortex has been in the loft for over 25 years, but I brought it down and fired it up and what do you know it worked.
            It's a little unstable but processing it probably has some capacitors that are a bit low but not bad for a home made machine stored for all that time.
            I think I will play with it for a while. I bought the mdex os for it I didn't really advance from the Cortex basic (that I quite liked) and I wrote a few programs for it, though there's none around now. I would like to get my hands on some software. I noticed earlier in the thread that there was a reference to WAV files of programs. Are any of these available and if so whereabouts can I find them?

            Norvin

            Comment


              Glad to know another machine has survived, Norvin! Is it possible you have any of the Cortex User Group newsletters? There are a dew we're still trying to track down. As to WAV files, I believe there are some in the Cortex folder at the WHT site. There are also disk images at Dave Hunter's Powertran Cortex site. I've included links to these sites and also to Stuart Conner's Cortex site here below:

              http://www.avjd51.dsl.pipex.com/powe...ran_cortex.htm

              http://www.powertrancortex.com/index.html

              ftp://ftp.whtech.com/Powertran%20Cortex/

              That's pretty much everything on the net with the exception of this thread and a few minor references at other computing sites. There are still a few NOS board sets (without cases or components) out there from the guy who turned up six sets a couple of years ago (he recently turned up three more sets of boards in his loft). They're a bit pricey, but he's got the only bare board sets left.

              Dave also has the MDEX stuff, so you might want to compare notes with him to see if you have any components he hasn't documented yet. His site also has a list of all of the newsletters we've turned up and put online to date.
              Enter My Mind At Your Own Risk!

              Comment


                Welcome, Norvin.

                Has anyone tried Dave's PC comms utility? I've got the source for Fig-Forth, TI Invaders and Tombstone City which should convert easily for the Cortex (they're already running on my TM990, so in theory I only need to change the VDP address, sort out a keyboard input routine, and slow the games down a bit). Dave's utility looks like a convenient way to actually load it from the PC onto the Cortex.

                Dave:
                (1) I'm assuming that your utility and the memory patches also work with the Monitor dump (L)oad command?
                (2) On my PC I've got some BASIC listings typed in from the magazines. If the user does a UNIT 2 on the Cortex, does your utility (or could it be easily modified to) send plain text, i.e. BASIC listings, which will be loaded as if typed in from the keyboard? This would be an easy way to load BASIC programs.

                Stuart.
                Last edited by Stuart; March 2, 2013, 10:23 AM.

                Comment


                  Originally posted by Stuart View Post
                  Welcome, Norvin.

                  Has anyone tried Dave's PC comms utility? I've got the source for Fig-Forth, TI Invaders and Tombstone City which should convert easily for the Cortex (they're already running on my TM990, so in theory I only need to change the VDP address, sort out a keyboard input routine, and slow the games down a bit). Dave's utility looks like a convenient way to actually load it from the PC onto the Cortex.

                  Dave:
                  (1) I'm assuming that your utility and the memory patches also work with the Monitor dump (L)oad command?
                  (2) On my PC I've got some BASIC listings typed in from the magazines. If the user does a UNIT 2 on the Cortex, does your utility (or could it be easily modified to) send plain text, i.e. BASIC listings, which will be loaded as if typed in from the keyboard? This would be an easy way to load BASIC programs.

                  Stuart.
                  My utility works with all SAVE/LOAD operations from BASIC and MONITOR. However, it does act as sort of an 'Intelligent Tape Recorder' whereby it decodes the header information so that it uses the Load/Autorun/Length/Checksum etc. parameters to automate the transfers.

                  I suppose I could add a sort of passive 'raw mode' where you would have Start/Stop controls and it would just record/playback any bytes it receives without doing anything with them.

                  Dave.

                  Comment


                    I don't think the WAV files are on the WHT site - I've had a look around but can't find them.

                    Comment


                      Originally posted by andyp View Post
                      I don't think the WAV files are on the WHT site - I've had a look around but can't find them.
                      I've not come across any others either.
                      I've a couple on my site, Wav's of the colour bar and tape test programs from the build manual.
                      Slightly more organised now at http://www.quantums.info/oldcomputers.htm

                      Jim

                      Comment


                        Hi, I have (and am currently scanning) the user group newsletters 1, 5 and 8. Who should I email them to so that they can be added to the website?

                        Steve

                        Comment


                          Originally posted by g7mmj View Post
                          Hi, I have (and am currently scanning) the user group newsletters 1, 5 and 8. Who should I email them to so that they can be added to the website?

                          Steve
                          Wow, great news, especially issue 8
                          I'm happy to host them for others to download and put on their appropriate sites.

                          Thank you very much for taking the time to scan them.

                          My email is jim@quantums.info

                          Many thanks,

                          Jim

                          Comment


                            Newsletter 1.zip

                            Newsletter 5.zip

                            Newsletter 8.zip

                            Here they are as raw BMP pages, PDF's should be here soon.

                            I'm off to read them now, many thanks Steve.

                            Jim

                            Comment


                              User Group News Letter 1.pdf

                              User Group News Letter 5.pdf

                              User Group News Letter 8.pdf

                              These are them as PDF's.

                              Jim

                              Comment


                                Originally posted by g7mmj View Post
                                Hi, I have (and am currently scanning) the user group newsletters 1, 5 and 8. Who should I email them to so that they can be added to the website?

                                Steve
                                Wow, superb! Thanks so much.

                                Dave.

                                PS: Thanks Jim for getting them on the Forum.

                                Comment

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