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Post by buzbard on Jul 15, 2016 22:12:01 GMT
I have 3 flat C128s, I don't have any Ds or DCRs. From what I understand the DCR's come with 64k of VDC RAM and the Ds and flats come with 16k.
I know that VDC register 28/$1C is set by the KERNAL ROM to indicate the type of RAM used.
The address in the KERNAL ROM that sets register 28/$1c is at 58151/$E327
Every C128 KERNAL ROM that I've seen so far has the value 32/$20 at this address which would indicate that only 16k of VDC RAM is installed.
So, I modified the C128 KERNAL ROM by changing the byte at offset $2327 from a $20 to a $30 and burned it to a 27128 eprom and placed it in my flat C128 just to see what would happen.
With only 16k of VDC RAM the 80 column screen was mangled, it didn't work. I plan to upgrade the RAM to 64k and try the eprom again.
But what I'm wondering is, what value is at 58151/$E327 in a stock DCR? Is it $20 or $30?
If any of you DCR owners (with stock KERNAL ROM) could type: ?PEEK(58151) and let me know the value, I'd appreciate it.
Thanks
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Post by ken on Jul 15, 2016 22:20:23 GMT
I got 32 from my 128dcr
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Post by buzbard on Jul 15, 2016 22:49:23 GMT
Thanks for the fast reply.
So Commodore didn't even change the KERNAL ROM to reflect the 64K?
That's to be expected though, I guess.
Are you gonna have any more of the VDC upgrade boards available in the near future? I don't see any listed currently.
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Post by ken on Jul 15, 2016 22:53:13 GMT
c= did not change the rom
just solder in the 2 new mew memory chips
or plug in a vdc memory upgrade board
and you will be good to go
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Post by ken on Jul 15, 2016 22:57:54 GMT
Thanks for the fast reply. So Commodore didn't even change the KERNAL ROM to reflect the 64K? That's to be expected though, I guess. Are you gonna have any more of the VDC upgrade boards available in the near future? I don't see any listed currently. I have 80 more here some built/tested and a lot of blank boards I am just way behind in building stuff , I am playing with all the new cartridge boards I had ordered I also got the M5 board if you dont have 1 yet...lol contact me off ebay and I will give you a discount |
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Post by buzbard on Jul 15, 2016 23:12:47 GMT
Cool, thanks. I've been wanting an M5 as well.
Probably after Monday though, kinda tied up for the weekend.
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Post by buzbard on Jul 25, 2016 22:02:00 GMT
Update: so the VDC upgrade board arrived (thanks ken!) and I installed it.
Removing the 8563 was kinda scary, I half expected it to snap in half at any second, since it's such a long chip.
I retried the patched kernal rom (that I made, from above) and it works great. All test programs so far report 64k, no problem.
Still not sure why Commodore didn't patch the rom for DCR units, laziness I guess.
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Post by Pyrofer on Oct 23, 2016 22:27:04 GMT
I need to patch that location too on my upgraded flat 128. Is the location the same for Pal/ntsc roms?
There are a couple other changes I need to make such as telling the machine it's PAL not NTSC as I burned the wrong rom last time and now the ToD runs fast...
Is there a good guide to the 128 rom and what is where?
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Post by 8bitheaven on Oct 31, 2016 20:12:30 GMT
I get 32. I have extended video ram(64K)
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Post by gsteemso on Nov 12, 2016 19:21:03 GMT
I periodically toy with the idea of a vastly improved ROMset for my 128s, which would remove as many flaws and annoyances as possible without altering software compatibility (of course, programs which ignore all sanity and jump directly to random locations in ROM are, as always, out of luck). One big item on the list of requirements for such a thing is a test for how much VRAM is physically present before setting that register appropriately.
I never could figure out why that test was left out in the first place, or at least the second place; you'd think that being able to use the same physical part whether assembling a 128 or 128D would have been a gain in production efficiency. Or was the 64KiB model produced only after the others had been discontinued?
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