Nintendo World Championship 1990 - reverse engineering

Nintendo World Championship 1990 - reverse engineering
by on (#242363)
One guy asked me to analyze this cartridge. Fortunatelly there were photos of PCB on the web so I give a chance.
There is one think I cannot agree with the Mapper 105 description:
Quote:
On powerup and reset, the first 32k of PRG (from the first PRG chip) is selected at $8000 *no matter what*.
PRG cannot be swapped until the mapper has been "initialized" by setting the 'I' bit to 0, then to '1'. This
toggling will "unlock" PRG swapping on the mapper.

Because the MMC1-PRG-A14 is directly connected to both EPROMS, if MMC1 is switched into 16K+16K mode and MMC1 PRG's bank is modified, $8000 might stop pointing to first 32k even without rising edge on `I` bit.

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Re: Nintendo World Championship 1990 - reverse engineering
by on (#242365)
Probably pull-up resistors are missing for 74hc30
Re: Nintendo World Championship 1990 - reverse engineering
by on (#242368)
Yes sorry, I did not notice there is VCC pull-up 4xresistor ladder above the switch (if that were LS, not HC - pull-ups wouldnt be needed)
Re: Nintendo World Championship 1990 - reverse engineering
by on (#242371)
Those 4-in-1 resistor components are called "resistor networks".
A resistor ladder is something else (a circuit related to digital/analog conversion).
Either way, it's hard to see on the photo, I wasn't sure what you were talking about, until noticing the "shadow" behind the DIP switches.
Re: Nintendo World Championship 1990 - reverse engineering
by on (#242377)
Kevtris' writeup mentions the cic reset line is connected to something else on the board, what's going on with that?
Re: Nintendo World Championship 1990 - reverse engineering
by on (#242378)
CIC reset is used to force the game into the menu on reset, instead of using a diode, resistor, and capacitor to detect A0 or M2 going high impedance.
Re: Nintendo World Championship 1990 - reverse engineering
by on (#242379)
I fixed the schematic - pin 7 of CIC is the one used to detect reset and which comes from edge connector, not pin 9.
Image

I like how Nintendo routed all pins of all chips either out of the board or to to a place where a hole was drilled,, even those non connected to anything to short them while gold plating. That helps in guessing!