VIC-1210 3K RAM Expander with RTC V-Link

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Mike
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Post by Mike »

sjgray wrote:So, my guess is this cart works in conjunction with the commodore vic1112 IEEE cartridge. I just picked up the 1112 cart and I have a regular 3k expansion cart but I'm not too familiar with the internals. Is there an empty rom socket inside? If so I could try burning an EPROM from the dump and give it a try ...
I found the following information in the Commander magazine 04/05 (download) on page 56 postscripted to a review about C64-LINK:
Commander magazine wrote:This review was originally to describe the V-LINK cartridge for the VIC-20. It is a functionally similar device, but is now being redesigned by Richvale to work totally through the expansion port rather than partly through the user port. The unit I have is of the earlier design, and consists of a standard cartridge, which added RAM (3K, 8K and 16K versions available). The ROM with the added code is fitted inside the cartridge. Connection to IEEE, parallel printer or modem is effected with an (extra cost) adapter(s) plugging into the user port. Hence, no IEEE disk can be combined with a parallel printer simultaneously. No networking provision is built-in. There are two bugs in the code: catalog with no disk connected hangs the system instead of giving an error message, and some of the Basic 4.0 statements don't work properly after IF/THEN. (Both of these were corrected in the C64 version). I'd suggest waiting until the new version is available. As of this writing, I do not know the release date for this one.
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eslapion
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Post by eslapion »

I suspect its from this sort of cart the BASIC V4 for the VIC I dumped many years ago came from.

I was given to me back in 1985 by a prominent member of the Sorel VIC-20 club.

He simply said this came from the University of Montreal.

Link to archive I made back in 2006 is here

I know the UdM had VIC-20s with IEEE drives attached to them back in late 1981.
Be normal.
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srowe
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by srowe »

I've found a mention of the V-Link on page 40 of this magazine.

There's also pictures of the C-64 version here along with a ROM dump. The pictures are useful because they seem to confirm my hunch that the code works with a single 6520.

At the end of the VIC BASIC4 ROM are the letters "DF ", the C-64 V-Link ROM has the more complete "DF RTC". I think that clearly identifies David Foster of Richvale Telecommunications as the original author of the VIC BASIC4 ROM too.
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Mike
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by Mike »

I'm glad this thread helped to uncover the likely originator of this BASIC extension. It is, however, also possible that CBM offered the core of this extension (just the V4 commands) in source code form to licencees, so they could extend it to suit their own needs.
Mike wrote:In the range of $A100 to $A500 I found lots of reference to addresses $935x which seem to act as some I/O registers - quite strange, as on an stock VIC-20 this range ($9200 .. $93FF) points to unconnected memory. [...]
In the meantime I found out, that the VIAs also appear in $9200..$93FF, and those addresses are just other mirrors of VIA #1 ($9110) - presumably used for obfuscation. :?

There are still those VL-1 or VL-2 cables necessary at the user port to use IEEE functionality, and as IEEE requires quite some extra signals beyond the 8-bit parallel data, those "cables" must contain extra circuitry. Possibly using the 6520 you mentioned.

...

BTW, it's either V-Link (of course, the "V" from the VIC-20) or C64-Link. No "C-64 V-Link". ;)
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by srowe »

Mike wrote:I'm glad this thread helped to uncover the likely originator of this BASIC extension. It is, however, also possible that CBM offered the core of this extension (just the V4 commands) in source code form to licencees, so they could extend it to suit their own needs.
That's possible but the copyright page of the C-64 LINK II claims copyright for RTC only. I think if they had sublicensed any CBM code then they would have been obliged to recognize that in the documentation.
In the meantime I found out, that the VIAs also appear in $9200..$93FF, and those addresses are just other mirrors of VIA #1 ($9110) - presumably used for obfuscation. :?

There are still those VL-1 or VL-2 cables necessary at the user port to use IEEE functionality, and as IEEE requires quite some extra signals beyond the 8-bit parallel data, those "cables" must contain extra circuitry. Possibly using the 6520 you mentioned.
The primary difference in the V-Link ROM and eslapion's ROM is the hardware accessed. As you've noted the V-Link one seems to access mirrors of VIA1 but the other code accesses a 6250 in IO2.

I guess, and it's only a guess, that this is what occurred
  1. RTC produced the V-Link, the IEEE cable attached to the user port
  2. Someone at the University of Montreal modified the ROM to work with different hardware based on a 6520
If the pictures that were posted on this thread some years ago were still available that could prove or disprove my assertion.
BTW, it's either V-Link (of course, the "V" from the VIC-20) or C64-Link. No "C-64 V-Link". ;)
Yes, I was being careless with naming.
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Mike
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by Mike »

srowe wrote:If the pictures that were posted on this thread some years ago were still available that could prove or disprove my assertion.
I had stored away those two pictures of the cartridge and the invoice:

Image

Image

Schema didn't (dare to) open the cartridge, as it was on commission from Syd's Personal Computer Museum, but I'd think it was a standard CBM +3K Cartridge with a 2732 in place of one of the socket places - it is then sufficient to re-route some traces to adapt the layout to a 2732 so the EPROM appears in the lower half of BLK5 (as described here).
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by srowe »

Good, that confirms there's no connector on the cart. I've not dug into the ROM in detail it certainly appears that data is read from & written to VIA1 DRB and DRA and PCR are used for the control signals.
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by srowe »

I've got my (nearly) complete disassembly of this ROM here
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by Mike »

Thanks for this.

From what I gathered from the other thread about the 4040, it seems this IEEE interface would really only require a 'simple' adapter cable on the user port with no active circuitry?

I'll have to check out once again how the S and L commands work in the built-in monitor. :)

And it should now be quite easy to produce a new version, that doesn't shot itself in the foot as a means of copy protection, by NOPing out the offending STx instructions. :mrgreen:
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Re: VIC-1210 3K RAM Expander with RTC V-Link

Post by srowe »

Mike wrote:Thanks for this.

From what I gathered from the other thread about the 4040, it seems this IEEE interface would really only require a 'simple' adapter cable on the user port with no active circuitry?
Correct, I'm not sure whether the pull up and pull down resistors will be need?
I'll have to check out once again how the S and L commands work in the built-in monitor. :)
They're documented in the manual for the C64 version here.
And it should now be quite easy to produce a new version, that doesn't shot itself in the foot as a means of copy protection, by NOPing out the offending STx instructions. :mrgreen:
At a minimum you'll need to
  1. knock out the "STA DBSEND" in VLVECTS
  2. knock out the "STA (VARPNT),Y" in LA73C
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