Re: 6561 Die Shot Reversing Explorations
Posted: Mon Nov 20, 2017 8:49 am
PM sentnorm8332 wrote:I also have a non-working 6560 I could part with if that would work.
The Commodore Vic 20 Forum
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http://sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?t=8733
PM sentnorm8332 wrote:I also have a non-working 6560 I could part with if that would work.
It's on its way. I sent it USPS first class mail, it should take only a week or so to get there hopefully. Thank you Kakemoms for giving this a try! I still have another one if needed. They are nearly impossible to find online short of buying another Vic. It took me 6 months to finally find some on e-bay and those are gone now.lance.ewing wrote:Fantastic news! Made my day. I was going to see if I could buy one online and then donate it to the cause, but that was probably going to be expensive.
Yeah I saw that too...Just wish they had an actual picture and knew the correct manufacturer, but I'm sure it's fine. Just make sure to check the return policy.lance.ewing wrote:There are some available below if anyone is looking for one:
https://www.littlediode.com/components/6560-101.html
I have decided to present the diagram that I have at the moment for the vertical counter reset logic, even though it still doesn't make sense to me. I have a feeling that I have reversed part of it incorrectly, but I'll post what I have and will come back to this post at a later point when and if I discover what it is that I've got wrong. I want to post it now because I've already moved on into other parts of the chip (like the cell depth counter and horizontal cell counter) and want to start posting about what I've discovered in those areas. I didn't want to leave this vertical counter reset logic out of sequence though.lance.ewing wrote:I still haven't completely worked out what is going on in the vertical counter reset logic. What I have so far isn't making sense compared with what I think I know about how it should work.
I have found this down-counter now and it will be the subject of my next post. I think it is what the datasheet calls the "HORZ CELL CNTR", although the block diagram differs a bit from what I'm seeing (I'll discuss those differences in the next post). From what I can tell, it looks like the reload or latching happens at the same time that the horizontal counter is reset to zero. Mike, would that make sense based on PAL VIC programming observations? I guess it would mean that within those initial 12 cycles of horizontal blanking for a line, any changes to the number of columns would be ignored (and obviously also for the rest of the line).Mike wrote:At some time in the raster VIC-I needs to reload/latch the number of columns for a down-counter ("number of columns left for display") - preferably shortly before the border colour could be displayed.
I can now confirm that the output of the logisim diagram that I previously posted in relation to the Cell Depth Counter reset logic is only half the story. The output of that previous diagram is indeed simply the "last value" of the CDC. There is a NAND gate and inverter combination (i.e. net effect an AND) that generates the actual CDC RESET signal:lance.ewing wrote:I wanted to make a note that I'm aware that although the cell depth counter reset logisim diagram above shows that the output will go high when the cell depth counter is either 7 or 15 (depending on D), obviously the cell depth counter won't fully reset until the end of the current line. So there must be a bit more to how the reset works. This output going high doesn't directly reset the counter. What I'm thinking now is that rather than being a reset signal, it is more of a "last value" signal. If this is high and "something else" happens, then it will reset.