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Post by mrbombermillzy on Feb 26, 2020 20:47:56 GMT
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Post by mrbombermillzy on Jan 4, 2020 14:16:24 GMT
Yeah, that makes sense but DPSRAM is still awfully expensive. The SRAM I put on SaRuMan-VDC exists in much faster variety, as fast as 12ns. It would be more technically complex but considerably less expensive to allow access to the same SRAM between the cycles used by the VDC and also during the HBI and VBI. The loss in speed wouldn't be much. I know Gideon Zweijtzer (64 Ultimate and 1541 Ultimate) created a VHDL version of the REC which uses SRAM.
Thats another way of doing it.
Im more an assembly coder, so you may have to forgive me if I may not be able to brainstorm the design fully.
What you describe above sounds like perhaps DDR RAM, except you would be writing BOTH cycles when in HBL/VBL. Am I seeing it correctly?
Perhaps a circuit with Gideons REC chip implementation included with the fast RAM would be something like what I had in mind as an end goal.
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Post by mrbombermillzy on Jan 3, 2020 19:35:19 GMT
The '68 is used on the C128DCR which already has 64k of separate VDC RAM so I don't get the point. Also, dual port RAM could potentially be useful for greater speeds on the C64 and VIC-20 where RAM can be shared between the CPU and video chip but the VDC has RAM all to itself so what could possibly be the point of having dual port RAM with a VDC ?
There are many reasons for doing this. Its not about the amount of RAM.
If you recall, the VDC RAM is a bit of a 'walled garden'. i.e. you have to jump through hoops to change anything and even then, it wont be done in a hurry. (special techniques can be used to 'burst fill' the RAM quicker, but even still..)
Having an interface to the (faster) RAM would allow it to be accessed by another entity other than the VDC and at a higher speed.
Im thinking cartridge memory space, REC chip, etc.
Basically, the VDC RAM could be used as a double/triple screen buffer while the actual VDC just 'shifts' the data out. (The REC can even be used as a sort of blitter chip with some scope for better software sprites).
I know it would be some work to interface, but, hey, Im just saying thats what I would like! I think both a REU cart and a final chesscart could make for some interesting scenarios with this sort of hack.
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Post by mrbombermillzy on Jan 1, 2020 10:06:11 GMT
What Ive always wanted to do is a '68 version of this, fitted with dual ported VRAM with some form of easy interface connector for future hacking purposes!
If I had the earlier VDC (or infact ANY working 128 machine! lol) I would buy this. Its very reasonably priced. Great work!
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Post by mrbombermillzy on Dec 4, 2019 19:03:04 GMT
Thats a kind offer Robert. You know what? If I cant get it sorted out by then I will take you up on that!
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Post by mrbombermillzy on Dec 3, 2019 9:32:18 GMT
Thanks Robert. I already have a 'custom' PSU in there which I fitted myself as my original board had cracked and split in half. Ideally, I was after a unit from this side of the pond. Getting a unit custom built by Ray and having it shipped from the US is probably a bit too steep for my budget. But thanks anyway.
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Post by mrbombermillzy on Dec 1, 2019 18:37:36 GMT
Thanks for the link. Robert B pointed me to this last time I asked. Unfortunately, the 105v input is no good for the UK, so I have to keep looking.
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Post by mrbombermillzy on Nov 27, 2019 20:14:46 GMT
Has anybody done any experiments with faster refresh rates and the 1084s.. the above put it into NTSC 60hz mode. But if we start cutting down the number of rows, vblank time etc can we start push it up to 70hz??
I experimented with lower scanrates when pushing max H pixels and severely reducing Hsync pulsewidth. As I wasnt using a scope, I guessed I was getting around 11-13Khz. Pushing it in the other direction could increase VBlank rate. However, you would then start losing some Horizontal real estate. Perhaps a H res. of 512px is a good compromise?
If you could get to 75Hz you could also triple dither for lots more colours (with the same amount of flicker) or have the 240 ish colours but a reduced flickering.
Its a shame theres not some sort of reset bit on the VDC which forces a VBL. This would be very handy too, as it would increase the Hz more dramatically.
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Post by mrbombermillzy on Nov 26, 2019 11:49:29 GMT
It would be great if anyone has a UK/EURO PSU for a C128DCR at a reasonable price.
Its been too long! I need to get back to my 128DCR!
Many thanks for any help.
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Post by mrbombermillzy on Nov 26, 2019 11:15:04 GMT
@pyro: The method I suggested would actually allow 16 colours on NTSC monochrome output 'as is', with up to ~240 with interlace temporal dither techniques. The interlace dithering methods as shown by ozi with regular RGBI output should display a higher resolution image, if not more colour as it is using proper colours. The mono method is using the colour error from a pixel pattern for colour, so resolution is much lower. Its a bit like a poor mans Amiga HAM I suppose! lol. There must still be quite a few people in UK/Europe who have TV's/Videoplayers/DVD players with NTSC signal selection as an option. Maybe the target audience isnt so low (as in some of euro/uk as well as USA). oziphantom : Do you mean something like a framebuffer?
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