Denial

I am able to answer a few of your questions. Hopefully I'll get a chance to go into the details over the weekend. For now I thought I'd mention that the output of the 16-bit LFSR, i.e. from the first bit, then directly controls the shifting of the 8-bit square wave shift register. What I mean is tha...

Yeah, I think so. It might not be obvious from the diagram, but the signal value going to the NOR gate from each bit is the inverse value. So when the counter is 127, then each of those inputs to the NOR gate is LOW, so the output of the NOR is HIGH. It appears that the output of the NOR also goes t...

I'm going to look over that section of the die shot again to confirm this, but at the moment I think we can say that part of the bottom half of the pink box is the 7 bit counter. Having re-checked the diagram of the 7-bit counter from that older topic from 2016, it is mostly correct. The only thing...

I did start to look at the area inside the pink box for the noise voice a few years ago. That discussion starts with the following post on a separate thread: http://sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?f=11&t=7118&p=88489&hilit=FPGA+6561#p88380 When I wrote the posts on...

I thought I'd post an image showing where the sound generating parts of the 6561 are located: noise_lfsr_highlighted.jpg The light blue boxes are the four control registers for the four voices, with CR-C the left most, then CR-B, CR-A and then CR-D (i.e. the noise register) being the right most. The...

I already know where the four control registers are, and I'm pretty sure I've just found a 16 bit shift register next to the control register for the noise voice. I'm still reversing the logic at the moment, but it is definitely a shift register, and I can also see a bit of feedback going on. So I t...

Not completely. I was partway into the sound generation a few years ago but didn't complete it. But its now the largest of the remaining parts of the chip to look at, so it will probably be the next thing I look at.

How expensive is very expensive? Where would the seller have got this from?

This is totally unrelated to the VIC 20, but I thought that a few people might be interested in this. I discovered this only a couple of weeks ago. I am originally from New Zealand. I was born there, grew up there, went to school there, started working there. Up until about 10 years ago I was still ...

http://sleepingelephant.com/ipw-web/bulletin/bb/download/file.php?id=2594&t=1 The main thing I wanted to draw your attention to in the above image though are the contacts I have labelled 1, 2, 3 and 4. I have assumed that they are redundant and have no purpose, but this seems a little strange t...

The program shifts the paddle value by 5 bits to the right, ORs in #$18 (white background, non-inverted) and writes the result into the border/background colour register. It's quite easy to find paddle positions, where the border colour differs between DMA and non-DMA parts of the screen: This is q...

Here is another version of the schematic with the various points labelled: pots_bias_and_vref_schematic_3.png And this is an image of the area of the die shot showing where these same points are, labelled with the same colours and letters: bias_and_ref_points_labelled.jpg We can see from this that t...

I just bought one of these too and I was wondering, would the board fit inside one of those new c64c cases if I were to dremel out the back for the cartridge slot? That's kind of what I did with one of mine, except that it was an original C64C case: http://sleepingelephant.com/ipw-web/bulletin/bb/v...

This evening I'll only get a chance to add the following version of the VREF and BIAS schematic with the dimensions of the various transistors shown, the width being the top number, and the length the bottom number: pots_bias_and_vref_schematic_2.png I've read that the resistance of these transistor...

It was certainly unexpected for England to beat Columbia in a penalty shoot out, but I've got to say that the English goal keeper isn't looking too bad in the game against Sweden today. He made some pretty good saves. Although I'm supporting England this time around, my home team is New Zealand, and...