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Last updated on Oct-18-2019 Download

Gutting a cheap Famiclone - exposing the connectors.

Gutting a cheap Famiclone - exposing the connectors.
by on (#139613)
Hey there,

Some few months ago I bought myself two Famiclones (Nintendo on a Chip ones), and I sacrificed one to do a nasty experimentation - rip out the guts of the console, and tear out the cartridge connector by desoldering it.

Looking at the common cart pinouts for the 60-pin ones, I saw all the pins from the address pins and the data pins seperately laid out (I guessed).

So I think it may be a fun idea to connect the CPU's D0-D7, and A0-A14 to a ROM and try to access the APU first. (Other pins like Chip enable are involved too)

I've used an SRAM pretending to be a ROM and I used a microcontroller to load up the code into the SRAM, and then let the gutted NOAC run it.

You think it's possible? It may sound really strange and it may or may not work. :D
Re: Gutting a cheap Famiclone - exposing the connectors.
by on (#139618)
If I understand correctly the problem with this is that the 6502 controls the bus at all times, so by trying to write to the APU you will be fighting the CPU on the address lines, inactive or not. Since the two are both on-die it's not like you can just disconnect the CPU.
Re: Gutting a cheap Famiclone - exposing the connectors.
by on (#139622)
In other words, the "SRAM pretending to be a ROM" technique (also used by the PowerPak) is probably the most reliable solution.
Re: Gutting a cheap Famiclone - exposing the connectors.
by on (#139642)
Unfortunately, you also can't reset the CPU—or even stop clocking it—when you want to write to the RAM. You should be able to slow down the master clock by enough to give the microcontroller enough time to emulate a ROM, but that will also change the pitch of the APU, as well as the speed of the sweep units.

Probably the most robust solution is a ROM (or preloaded RAM, which I guess lets you easily reconfigure DPCM samples) that contains the a tiny IRQ handler that's something like
Code:
pha
txa
pha
ldx $6000
lda $7000
sta $4000,x
pla
tax
pla
And a little bit of hardware (74'139, two 74'244s) to map one 5- and one 8- bit port from the microcontroller to memory ranges in the CPU's address space. Whenever the microcontroller wanted to write to the APU, it'd just pull /IRQ low and release it after ~10ish M2 cycles.
Re: Gutting a cheap Famiclone - exposing the connectors.
by on (#139654)
@tepples: I wished I got that PowerPak, but the problem is, I'm living in SE Asia and the shipping can get really expensive.:)

@lidnariq: Thanks for the explaination. Right now I built the "emulated ROM using an SRAM", and then directly connect the address lines and the data lines and see what would have happened. I'll try your sample code and see if it could squeeze out a beep or two. :)
Re: Gutting a cheap Famiclone - exposing the connectors.
by on (#139655)
The_YongGrand wrote:
@tepples: I wished I got that PowerPak, but the problem is, I'm living in SE Asia and the shipping can get really expensive.:)

The Everdrive N8 is as good as the PowerPak, and the shipping is very cheap.
Re: Gutting a cheap Famiclone - exposing the connectors.
by on (#139803)
Not to mention that its price is lower and it comes in both 60-pin and 72-pin versions.