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alex_79

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About alex_79

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  1. Chapter 2 of the Magicard manual explains how to safely handle the bare board, which orientation is the correct one, and how to open the cart port dust cover using a fiberglass tool included in the package: You can find scans of the manual here on AA: https://www.atariage.com/manual_page.php?SystemID=2600&ItemTypeID=&SoftwareLabelID=281&currentPage=15&maxPages=138&currentPage=0 I made a PDF version of the manual a few years ago, that you can find in this thread: https://atariage.com/forums/topic/233941-magicard-pal-conversion-enhanced-version/
  2. It seems that the TV is on the wrong channel. Are you sure that you tuned it correctly?
  3. You're right. Here's an excerpt from the "Berenstain Bears" game manual mentioning this "feature":
  4. Weird. In the Tapper rom that seems to work fine on this board, the next instruction is at $fff9, so both A6 and A5 are HIGH. I didn't include it in the schematic (as my goal was just to determine the truth table), but in the pics there's a small ceramic capacitor (unknown value) between pins 10-11 of the 74LS00 and GND. Could a cap placed there help filtering out transient variation of the /R and /S inputs due to A5 and A6? And, if so, could it be that it works when A12 pulses LOW, but it's not enough when A12 is steady LOW because the effect of the other signals (A9,A10,A7) are delayed by the extra gate (of the 74LS10) they go through compared to A12? Sorry for the likely dumb questions. As I've said I only have very basic knowledge about this stuff, but I find it very interesting nonetheless.
  5. It doesn't change the truth table: in both cases (pin 4 floating or connected to pin 5) the gate acts as an inverter for the signal on pin 5. Whether it affects the timing during the transient, I have no idea.
  6. I guess it's a timing issue: the address lines don't switch state all at the same time, and the logic gates themselves add delay to some of the signals too. When accessing the hotspot from RAM, A12 stays unset, and maybe during the transition of the remainig bits between the valid hotspot address and the valid next instruction one, a pattern corresponding to the other hotspot (or the "illegal" state of the latch) briefly appears on the bus, messing the bankswitch. This is just my naive theory, so don't take my word on it! I'm able to trace the circuit and reconstruct the truth table based on how the logic gates are wired, but understanding what happens during the transients is well beyond my skills.
  7. The highest address pin (A14 - pin 27) is tied to +5V, so the Atari only "sees" the second half of the eprom. What's in the first half doesn't matter. Yes, you can put a 27128 in there without modification. I don't know what's the purpose of those resistors.
  8. Yes, each eprom contains half of the rom. As for replacing it with another game, it's no different than for the other boards: you can as long as the game uses the same bankswitching as the old one. If not, it has to be hacked first. Popeye cannot be converted to work on any of these boards. The bankswitching it uses is very different and more complex than the one used by Atari. (instead of 2 4k banks, there are 8 1k ones that can be mapped in any order in the Atari 4k address space).
  9. Regarding for the "Kangaroo" board, the rom is split into two 4k eproms. The bankswitching logic switches the "chip enable" pins of the 2 eproms so that only the one containing the current bank is enabled. Some commercial Atari 7800 and atari 5200 games have the rom on separate chips. And the typical board used for 2600 8k prototypes has two 4k eproms too (here an example).
  10. I'm glad it finally worked! So it seems that the bankswitch on this board doesn't work reliably if the code that accesses the hotspot is being run from RAM. In the last version of "Tapper" it has been changed to run from ROM.
  11. Very interesting, thanks for sharing! That one with the touch switches is really cool! Never seen a 2600 cart like that.
  12. Another try... tapper_fa0_v3.bin
  13. You're right, and I'd have expected pins 4 and 5 to be connected together too. But the pictures with the IC in place showed no solder on pin 4 on either side of the board, and another similar PCB documented a while ago leaves an input of a used gate floating too, so I thought they did the same here. Note that in both cases they could have connected the floating input to a pin right next to it.
  14. Many thanks for taking the pics of the board with the logic ICs removed! This confirms that the schematic I posted above is correct. Not sure why Tapper is not running on real hardware. I'll look into it. I'm glad that at least the other roms are working.
  15. There are a couple of errors regarding the 2600 in chapter 8: The console is from 1977, and the 6507 has 13 address lines so it can address 8k of memory
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