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Memory and Video Expansion


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I was in a conversation at the MEGA65 discord server where someone was talking about other cores they'd like to see made available, as MEGA65 is FPGA and can take on multiple personalities. C128 came up, which is near and dear to me.

The MEGA65 has two video output ports on the back, an "IMDH interface" (non trademark encumbered equivalent of HDMI) and a DB15 VGA interface. They both show the same screen in the MEGA65, but since it is FPGA, there might be a chance they could actually support two different output signals if the core supported it. That is unknown, but an interesting thought.

Bringing it back to Commander X16, I mentioned that there has been discussion of putting VERA on an expansion cart for C64 or other expandable systems. MEGA65 has a C64 compatible expansion port so it seems to me it *should* be possible to plug such a beast into MEGA65 and have it work, maybe.

While we were talking, I had two thoughts come to mind for display expansion. The first one was Commodore 8-bit computers and similar "compatible" systems like MEGA65 & X16, will have an IEC serial bus for talking with external drives and printers.

Why not create an IEC serial "printer" that is actually a second screen? It would be slow, yes, but I can imagine ways to use it that would be very useful, such as debugging output while the VIC is busy with the actual application. And since the IEC bus supports daisy chaining, it could support more than one such display if desired:

10 OPEN 4,4
20 PRINT#4,"HELLO DISPLAY DEVICE #4"
30 CLOSE 4
40 OPEN 5,5
50 PRINT#5,"HELLO DISPLAY DEVICE #5"
60 CLOSE 5

Then I had another idea. We know C64 & C128 supported RAM expansion in various ways. 1700 series REUs, GEORAM, and RAMLINK to name a few.

What if in addition to that functionality, those devices also had one or more monitor connections such as IMDH, VGA, or some such. My main workstation at home is a four monitor rig with two landscape monitors front and center stacked on top of one another, and two more portrait orientation monitors to the sides. It would be interesting to have such a setup for a C64 or other system.

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On 11/3/2021 at 4:28 PM, Scott Robison said:

Why not create an IEC serial "printer" that is actually a second screen? It would be slow, yes, but I can imagine ways to use it that would be very useful, such as debugging output while the VIC is busy with the actual application. And since the IEC bus supports daisy chaining, it could support more than one such display if desired:

Or just use a serial terminal. Something like the GeofG terminal with a PETSCII character set would work very well. 

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All good variations on the theme. I think a serial terminal would be a great solution for that use case, just need a little logic (if on the IEC bus) to make it a "smart" device that "just works" with the C64 (or other IEC capable computer).

I've seen many solutions to a second screen that used the expansion port, but never anything that acted like a printer (or plotter). A "glass printer" would be nice on device 4 or 5, and a "glass plotter" on 6 or 7.

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