I guess I was trying to put myself back in the 1980's "be as compact as possible" mindset.

Though my Google-fu was not doing well last night, I did finally find the manual for this product:

https://colorcomputerarchive.com/repo/Documents/Manuals/Hardware/Green%20Mountain%20Micro%20-%20Lowerkit ...

I have used the 6847 before, but not with an external character ROM. I assume you are referring to the schematic figure 23 in the data-book? It may be a little confusing but data lines coming from the display memory need to be connected to the address lines of the character generator. The address ...

Hello Jim,

Maybe these (compiled pages from a datasheet) will help:

Thanks, but I already pored over the data sheet (downloaded). However, Rob Finch's comment about the data from the regular memory (which is addressed by the VDG) being used as the top 8 bits of the address for the external ROM ...

Looking to use a 6847 on a project, and wanted to try to use the external ROM for characters noted in the datasheet. But, I am confused about how to feed some of the character ROM address lines (the 8 that appear to be coming from the Data bus, but that does not make sense to me)

Anyone ever used ...

Will be there!
Fri/Sat/Sun
Jim

Search for the SixtyClone project, which is close to what you describe.

Jim

A PLCC is pretty compact, so it strikes me there's not much space saving by going to a QFP instead. But that's for you to judge. :)

Just remember that use of the -S part has different implications for the Port A and Port B lines than it does for the lines of the Bus Interface.

In all cases the ...

Are we talking about converters on the '22s interface to the micro, or the external-facing interface?

Either way, level shifting ICs are readily available, which handle 8 (or more) signals in one chip.

Not sure I understand your terminology, but the application would be a small PCB that plugs in ...

I expect there would be no problem, but I would have to experiment. It will come up fast to about 2.5V, a little slower to NMOS's and 74LS's maximum output voltage of what, maybe 3.5V?, and most slowly beyond that. IOW, a passive pull-up is not working alone until the voltage gets to about 1.5V ...

I wonder if passive pullups on the CMOS part would be fast enough on a 1-2MHz application... Current mirrors would be nicer, but could add significantly to the parts quantity and/or board real estate.

Jim

For space reasons, I would like to use a QFP-ish package for the 65C22 for a Commodore 1541 hardware enhancement. As many know, the NMOS-compatible 65C22N is not available in such a package, but only as PLCC and DIP.

I know about the IRQ line difference and how that can be addressed with a diode ...

Yep, I saw the 8 bit offset restriction, but I figured the table could start in the first 256 bytes... But, I also made sure the self modifying code in the 6502 case ran from zpage as well, since the inc of the memory would be faster, and I seem to remember one other opcode being faster. I figured I ...

I used words "rather mediocre" which give me some room for maneuvers. :) And BTW I have checked a dictionary and found out the next definition
The roots of the adjective mediocre are from the Latin medial, "middle," and ocris, "mountain." If you think about it, the middle of a mountain is ...

Also a good choice and somewhat more neutral.

Jim

Thank you very much for reading and valuable comments. Indeed my material shows my point of view, it can't be completely free of gaps in my knowledge. I have really try to use only correct data but my other purpose is to make the article emotional, so it contains unproven assumptions (which can be ...