XTAL clock and 2A03

I don't think this oscillator will work.

Use the recommended chip (or a ready made oscillator).

BUT..... you seem to connecting the Arduino to the NES chip as if the Arduino were a memory device - what makes you think this can work ?

MK

Thanks for the feedback. Recommended by whom? The 21.47727 xtal is the original one from the same board the 2A03 is from. I guess I should use the original boad as an example for the *** circuit rather then that link. I'll try to map that out then re-evaluate.

The idea was that the Adruino is faster (16MHz) then then 2A03 (~1MHz) so could use the readwrite line as an inturupt so when ever it goes high it triggers the Adruino to output on the 8 digital pins connected to the data bus, the next instuction or value I want to send to the 2A03 and at idle just send NOP then JMP to some starting address in a loop.

If the timing of all that doesn't / won't work I could hard code NOP just to see if the 2A03 is working.

The oscillator in the original article is a Pierce oscillator.

Do you have a logic analyser or an oscilloscope - if not then you have pretty much no chance of getting this working.

The Arduino is nothing like fast enough for this to work. I couldn't find timing information for the 2A03 but assuming it's like a 6502:

At 1MHz cpu clock you get 575ns read access time - about 9 processor cycles, during which time the AVR processor would need to

respond to an interrupt, set the bus direction, read the address, output the data and return from the interrupt.

It isn't fast enough, even if coded in assembler.

You could do it with a much faster processor but you would need to code it very carefully in assembler or C (not using Arduino environment).

An ST STM32F42x could do it, and could probably provide a suitable if not exact clock as well.

The NUCLEO-F429ZI (about £20) from Farnell would do nicely, the processor has 256k of RAM and clocks at up to 180MHz.

The coding will be non trivial - you won't be able to use the HAL routines provided by ST to operate the IO ports but will need

to code with direct access to the STM32F429 registers directly.

Once again, you'll need to be able to look at signals to get this working.

MK

Jan Cumps  wrote:

 

The oscillator in the original article is a Pierce oscillator.

It's the month of Project14 | Making Time: Anything that Uses or Alters Time such as Clocks, Timers, Egg Timers, and More! .

I'm going to try and make a single transistor Pierce oscillator. I've got a candidate design from a Linear Technology application note.

I've built one up on perfboard this morning, but haven't tested it yet.

Very coolly opportunistic !

I miss the nice old fashioned crystal cans - the little surface mount ones just don't have the same feel !

MK

michaelkellett  wrote:

 

Very coolly opportunistic !

 

Yes .

It works:

Is it an optical/camera illusion but the 4 cycles on the left lean to the left and the three on the right lean to the right !

BTW - the app note you linked is from National Semiconductors (now part of TI). Linear technology, another good US analogue semi

company, now belongs to Analog Inc.

In the good old days, (1970s) National were a real force - I still have some Data and Applications books from then.

MK

The leaning is a camera artifact.

This is a scope capture, with a 16 MHz crystal this time.

It's far from a perfect sine wave (for curiousity I turned on the FFT and there's a whole train of harmonics).

But the wave form is not the point here. It's a clock.

Certainly, I don't know if the 2A03 cares about getting a good square wave on its clock input - I haven't been able to find  a spec for it.

Which FET type did you use ?

MK