Jump to content


  • Content Count

  • Joined

  • Last visited

Community Reputation

89 Excellent

About AwkwardPotato

  • Rank
    Chopper Commander

Profile Information

  • Gender

Recent Profile Visitors

4,519 profile views
  1. If yours is actually labelled TMS9919 (which is actually pretty rare in 4As) it needs to be replaced with either an SN94624(A) or SN76494(A). Other chips like the SN76489 would need a higher clock rate than is found on a board that originally came with a 9919.
  2. ...and as far as I was able to tell, the parallel 4Mbit parts are listed as "Obsolete, Not Recommended for New Designs" on virtually all major electronics distributors, whereas the Spartan is still active and in stock. There's no question about whether such a thing will work; an EEPROM approach straight-up will not work in the 4A.
  3. I'm pretty sure he's not misunderstanding -- replacing one FPGA with a litany of EEPROMs is impractical at best. Most FPGAs remain on the market for quite a long time, and the task of reworking a board to use a different one would be far easier than designing this hypothetical, comically large EEPROM-based board. Parallel EEPROMs themselves are going out of style; Mouser only shows 13 different parts in stock in your suggested size. More importantly, EEPROMs are a poor substitute for programmable logic at the speed of the 9918A/F18A. The access time of 120ns for the part you linked (which is typical for EEPROMs of that size) means it'll take 120ns for the output data to be valid after an address change; by extension, a chain of 4 EEPROMs cascaded would need 480ns for the output to be valid, at which point you're almost certainly violating the timing requirements of the 4A.
  4. Unplug the power board from the motherboard. On the motherboard's power connector, measure the resistance between each of the power rails (+5V, +12V, -5V) and ground. Chances are at least one rail is shorted if it's causing the power board to buzz. Also, 11.7V is totally fine for the 12V rail.
  5. Small dabs of hot glue; if the glue needs to be removed, isopropyl alcohol will detach the drop of glue from the board without damaging the board or leaving any residue at all.
  6. You have to do a full transaction with each sensor to properly implement SPI. Sensors will not report data back to the AVR on their own; the AVR is responsible for clocking the data out of the sensors. The time it would take to query a single sensor is so small that parallelization is impractical.
  7. Implementing SPI does not have to be this complex. No 512-pin breakouts or latches or buffers are needed -- the sensors/displays/etc will not compete for control of the SPI bus, since the AVR will only ever read/write to one device at a time. Theoretically, to implement this you'd connect the 3 SPI lines (SCK, MOSI, and MISO) from the UberGROM's AVR to each SPI device in parallel. Each device does NOT need its own SCK/MISO/MOSI. An individual Chip Select for each device can either come straight from the AVR, or from a demux if you run out of I/O. If I'm not mistaken, the UberGROM could use the READY line on the cartridge port to slow the TI down for slow SPI accesses. With this method, you would need a total of 7 wires coming out of the cartridge for 4 SPI devices. If you wanted even fewer wires than that, you could use I2C instead of SPI, allowing access to up to 128 devices with only 2 wires.
  8. About the RPi Pico -- it's not in the same league as any of the other members of the Pi family, so using it for TIPI is likely out of the question. The core they're using on it is identical, for the most part, to the one found on higher-end Arduinos. What makes it interesting though is the programmable I/O, which has already been demoed driving HDMI displays.
  9. Yes. That component (it's an inductor, btw) actually looks totally normal. Even though the video works fine, it's worth reflowing the joints on the motherboard's video connector to rule out a bad solder joint as your sound problem. It's common for a cold joint to appear fine, when in reality it isn't.
  10. The highlighted component wouldn't affect the sound; it's part of the video circuitry. If you have a multimeter, plug in your video cable, and see if there's a connection between the center pin of the cable's audio jack and the video connector pins on the bottom of the motherboard. If there isn't, resolder the video connector pins.
  11. Rich hasn't done anything wrong, please get over yourself. These back-and-forths do way more to trash threads than RXB plugs.
  12. The PCB would be the relatively easy part; the hard part is coming up with new mounting hardware to install the PCB in the case (modern switches are lower profile so the whole board has to be raised up) and finding keycaps that look appropriate in the TI.
  13. Thanks, that makes more sense. I never knew the 99/4 could come with a 9928/29, everything I recall reading online suggested to me that they only came with 9918s.
  14. Wait, I thought all 99/4s were NTSC units with the original 9918, and European users could only use them with TI's NTSC monitor. But the GBS8200 doesn't work with the composite output of the 9918(A), it needs the YPbPr output from a 9928/29. Is the VDP that came in your 99/4 labelled as a 9918, or something else?
  15. I'm surprised that the European 4A had a 9918A in it, and that the 4 used to work with a PAL modulator, because both the 9918 and 9918A are NTSC chips. AFAIK TI never shipped a system with the 9928(A) in it. Sadly, most software that won't normally run on a 4 still won't run after installing a 9918A. Probably down to ROM/GROM differences. Glad to see that you found what was causing the keyboard problem, and to see the 99/4 mostly working
  • Create New...