nesdev.org

Since the registers used are: $9000-2 $A000-2 $B000-2 all but A13, A12, A1, A0 can be tied. Since A15 is multiplexed with M2, you may need to synchronize your writes to the clock if the registers are flip flops and not latches. If they're latches, you probably can just toggle "/PRG CE" to...

I haven't given up on this yet. I wired it up to a 1.84MHz oscillator and tied all the non-PRG chip enable pins high. I wired PRG CE and R/W low, and the result is that the pins are giving me output (some are high, some are low, I haven't decoded the actual address/data values yet). Why do I get dat...

I'm trying to get just enough control over a VRC VI chip to write to the sound registers with a microcontroller. I've read Kevin Horton's paper on the chip many times, but there are still many blanks for me. I'm a EE, and I use projects like this to gain better understanding of the CompE side. How d...

Oops, it looks like my writing process was also writing some garbage data between iterations. It seems to be working now

I had to take a break from this project because of school and graduation, but I'm back on it now :) Now that I can write registers, I am able to get sound out from the Triangle, Noise, and DMC channels. I tried this order for using the triangle channel: Write 0x7F to $4008 Write 0x11 to $400A Write ...

So I need to sample an analog voltage and scale the digital result to be base 2 logarithmic before it can set the pitch of an NES channel. I would not know where to begin doing that math in assembly Lookup tables. Lots of lookup tables. I wanted to make a lookup table that covered all 12 bits, but ...

If you're only making a music engine, I'd bet a 6502 C compiler would be fast enough. The problem is that it's not only a music engine; it's made to interface with CV signals on a modular synthesizer, in addition to reading rotary encoders. For example, synth modules use a standard pitch control fo...

DPCM can't be used no matter how it's done? Or is that only a problem if I use the microcontroller to tend the 2A03 directly? Since the microcontroller already has other data to be concerned with, and I don't know any assembly, Kevtris' circuit seems perfect. I put it together this week, and it's ge...

blargg wrote:First off, your switch statement is missing breaks, so every one falls through. Second, is the microcontroller fast enough?

Not sure how I forget every break statement, thanks for pointing that out. The micro is running at 40 Mhz right now, do I need it faster than that?

That "discrete ROM" approach is really simple. The '138 decodes the address into 8 individual enable lines, each of which "enable" that byte of the ROM. The two data values you provide are simple. The other values are gated by the remaining '245, and generated by a clever combin...

Thank you very much for that detailed post, kevtris! The reason I'm using a microcontroller is because I need a minimum of 6 channels A/D (pitch and volume for each channel), in addition to reading in several rotary encoders. There is also a lot of math in the pitch mapping that I need, and I would ...

Yesterday a parts order from Digikey came in, so I now have a 2A03 powered and clocked. If I check the address bus pins after it's been running, they read $FFFF. Does that mean the chip has already stepped through all the address values? When it turns on does it just count up through the address val...

Thank you for clearing that up! I've been working with Atari Pokey chips too, and on those the address pins are inputs so I mistakenly thought everything worked that way. So now I need to learn how to get code to the 2A03, or how to make the 2A03 execute code. I imagine this stuff is pretty basic, s...

There is NO I/O pins that allow you to directly write to the sound regs ($4000-$4015), instead you should have a programm that is read through the microprocessor's data and adress I/O, and that programm should write to it. I'm having some problems understanding the processor, I think. Please bear w...

Hello everyone, this is my first post here. I am working on a project that will interface a 2A03 with a microcontroller to make a synthesizer module. It will bring together what I already know about analog circuits and hopefully give me some new skills on the digital side. Right now my biggest probl...