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Found 7 results

  1. HELP! I've been working on this project: http://github.com/calphool/TRS80GS I've built 4 revisions of this board for my friend's TRS-80. I've had a heck of a time keeping the VDP chip working in a stable configuration. I had everything working for a while, and then suddenly it decided that it wouldn't work any more. I screwed around with the caps on the crystal (soldering on heavier leads and stuff), and eventually it blinked back to life, but now I only have a luminance signal (or at least the TV can't interpret the color part of the NTSC signal, so I get black-and-white). What I need is a very stable clock, and unfortunately there seem to be about a half dozen different examples of how people have set up the clock on this chip. Here are a few: I need something that just always works, not something that's flaky and subject to weird transient noise. The VDP and its clock divider are basically the heart of my board now, and if I can't get the clock working right, nothing works (the sound chips and UART chip use the divided clock signal that comes out of the VDP for their own clocks). What's the best way to make sure this clock is super stable and reliable? The Texas Instruments hardware design? It's got a bunch of stuff inline (including something it calls an "SR Inductor" that has no uH rating, and I'm a little confused by). The ChromaTRS design? It's got some inverter gates attached to the crystal (though it doesn't specify the value for the resistor it's using). I've been using variations on each revision, with the most recent being the one from Byte magazine, which is flaky as all get out.
  2. I normally don't like to announce things before they are ready, but I can't keep making excuses to those waiting and asking about the next F18A board run. For the last 6 months, while requests for the F18A were trickling in, I have been working on a new version of the F18A, called the MK2, to solve the problems of the current board. At the point were I had enough requests for F18A boards, I was not quite ready with the new MK2 design, so I continued to avoid the direct question of "when do you think the next F18A run will be?" To not have to keep making excuses, and with apologizes to those who have been waiting patiently for a long time, I'm announcing the F18A MK2 now, about a month before it will probably be shipping. I wanted to do this so people would have some real status, and to help my conscience (Vorticon, I spelled it right this time... ). Here is a link to the long version of the story: http://codehackcreate.com/archives/592 I'll do the short and sweet version here. The primary features of the F18A MK2 are: * It is 52mm x 19mm, i.e. the same size as a standard 600-mil 40-pin DIP socket, so no tall-pins, short-pins, adapters, etc. will be necessary for it to fit in the host computers. * Digital video output (TBD, probably DisplayPort). No, there is no VGA, sorry. See my post above for the details on that. Digital video to VGA converters are available if you really need/want VGA. * Host audio injection into the video signal for those who can manage to connect one wire internally to pick up the system's audio and get it to a pin on the MK2. The MK2 will run the same core as the original F18A, and I am still committed to supporting, working on, and fixing the original F18A issues (there is a known problem with the interrupt on some systems, etc.) Future features based on the enhanced MK2 hardware. Access to these features will come with future firmware releases (I don't have time to do it all at once, sorry): * The MK2 has 512KiB of 10ns SRAM, i.e. basically 512KiB of VRAM. This VRAM will be available in a 9938-compatible way, and then some. * The MK2 has extra I/O, including the Mode-1 pin to make it possible to do the 9938-update to the 99/4A in a "TIM" manner. * More than double the FPGA resources than the original F18A. This means more possibilities for new stuff in the VDP. Other non-TI related possibilities: * With simple low-cost adapter boards to re-arrange the wiring, plus a firmware change, the MK2 can be used to replace other VDPs like those in the NES, the Master System, MSX2 (i.e. 9938/59 system), etc. * Stand-alone FPGA-based game system due to the on-board 9900 CPU and 14 extra general-purpose IO pins. * General purpose FPGA devboard. * More simple SPI-based host interface to use the MK2 as a video chip for simple micorcontroller projects, i.e. Arduino, etc. I plan to keep this thread updated with status and to gauge feedback. If all goes well, and if I have not just made a big mistake, I hope to have the MK2 shipping by late July. Ironically this will be exactly 6-years after the original F18A shipped! Some renderings and photos of the current prototype:
  3. Hey all, Here is a question... so the TI disk system reserves space at the top of VDP memory for file buffers. You can reduce this by from 3 file support to 1 by calling the FILES subprogram, but it still takes up space from about >3B00 onwards. My question is... can you safely wipe out this section, say if you wanted to put the sprite pattern table at >3800 onwards? Obviously it would trash the sprite pattern table if you had to do a file load later on, but if you could restore the data from CPU memory afterwards it seems alright. Obviously it would be stupid to try and do a memory image load INTO this section...
  4. Does anyone have a datasheet for the 9918? Is there any pinout difference between the 9918 and 9918A? Also, aside from GM2, are there any functional differences? What I am ultimately trying to determine is if the F18A can be dropped into an 99/4? Has anyone tried?
  5. From the album: Repairing TI 99/4A

    An image of my TI 99/4A motherboard soon after I pulled the 8 VDP RAM chips (TMS4116).

    © David Vella

  6. Davvel

    ti99 VRAM 1

    From the album: Repairing TI 99/4A

    A few photos whilst repairing my TI 99/4A

    © None

  7. Check out this thread from the Colecovision forum: http://atariage.com/forums/topic/216268-my-first-test-on-the-tms9918/ Maybe this can be used also on our system? Both systems share the same VDP.
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