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6520 & 6526

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giobbi

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Dec 23, 2012
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São Paulo country, Brazil
Hi all,

hoping everybody is alive and kicking, I'm here with a question:

is there any modern replacement/adapter for 6520 and 6526?

There more or less a workaround for almost any C= chip: the RRIOT 6530 can be replaced with a 6532 [that's still in production by Rockwell, afaik] + eprom + logic glue... there's an adapter for use a 6502 instead of 6510/8501/8502 and there are some works in progress even for TED and VIC-II fpga replacements.

But I didn't find, in example, any "6522 to 6526 adapter", or any replacement for 6520... that's quit odd, IMO.
 
... As for replacing a 6526 with a 6522, that wouldn't fly, unfortunately. The chips are pretty similar but the 6526 has some features the 6522 lacks, like a Time-of-Day clock, and the register layout of the features that do overlap isn't 100% compatible.
 
Eudimorphodon said:
... As for replacing a 6526 with a 6522, that wouldn't fly, unfortunately. The chips are pretty similar but the 6526 has some features the 6522 lacks, like a Time-of-Day clock, and the register layout of the features that do overlap isn't 100% compatible.
Click to expand...
yep, the 6522 isn't a drop-in replacement for 6526 of course. But since (most of?) the 6526 unique features are rarely (or never) used by the C=64, I'm wondering if there's a way to make an adapter using a 6522 plus some logic glue.

I mean: if it's possible to replace 6510, 8501 and 8502 with a 6502 + logic, it should be possible to do the same with 6522 -> 6526... am I too optimist?
 
giobbi said:
I mean: if it's possible to replace 6510, 8501 and 8502 with a 6502 + logic, it should be possible to do the same with 6522 -> 6526... am I too optimist?
Click to expand...

It's not really a directly comparable situation. The 6510 is completely software compatible with the 6502, it just has a tri-state address bus and a couple I/O ports; making a 6502 into a 6510 is just adding hardware. (Some buffers and latches.) The problem with the 6522 vs. the 6526 is the latter isn't a "clean" superset of the former; even if you rearrange the pins you still have the problem that the registers have been rearranged. You'd basically have to stick a "command translator" in front of the 6522 in addition to implementing the missing pieces. To do that without a *large* circuit board is going to take programmable logic, and that point you probably might as well just clone the whole thing into a CPLD.
 
The 6520 can be replaced with a 6821. I could be wrong but IIRC there is a FPGA/CPLD replacement for the 6526. At least the equations exist, 64Ultimate etc.
 
I guess it depends what you wish to use it in, they work just fine in 1541's. But yeah 6522 equiv, not 6526 as I wrote - braino moment.
 
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