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Post by plbyrd on Apr 20, 2007 11:45:59 GMT -5
I keep seeing all the IEC projects based on ATMEL (and other) processors, but never one based on a 6502. Why is this? It would seem to me that using a 6502 based processor would allow someone to create a device that really does implement the IEC protocol exactly the same way Commodore did (h***, let's use the C= ROMs) and also would work with fast loaders, too. Would an FPGA based board be too expensive to do considering the plethora of 6502 implementations available?
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Post by David Murray on Apr 20, 2007 14:19:44 GMT -5
I was under the impression that there were almost no microcontrollers based on 6502 available. I think somebody pointed one out to me once, but I couldn't find anywhere that sold it.
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Post by plbyrd on Apr 20, 2007 15:07:03 GMT -5
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Post by gmoon on Apr 20, 2007 17:18:28 GMT -5
It's cost/convenience/complexity factors. Most current FPGAs have a pin count > 144, and are SMD. Any development work is done on a dev board with the FPGA in-situ.
If anyone wants to replicate your work, they'd need a dev board, too. Or a commercially prepared PCB with the FPGA installed. Not like grabbing a cheap 28 or 40 pin 8-bit micro controller and programming it yourself.
Even if you emul the 65xx on the FPGA, you'd need RAM, too. If you use a physical 65xx (ala minimig & it's 68K) it's a bigger chip count and a more complex build.
Given all that, I'm sure it's possible. But it would be a grand hack...
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Post by Jim Brain on Apr 20, 2007 23:15:01 GMT -5
The only uC based 6502 is the 65134 from WDC. But, it was designed in the late 1980's, so it does not offer many of the neat things we take for granted in uC offerings today.
o It has no Flash for code storage (the masked programmed ROM inside it is useless for most things, and there are only functions in that ROM, not a true program) o It contains very little RAM (256 bytes, as I recall). o It also does not support setting IO pins for HiZ operations, needed for IEC implementations. o It's only offered in a 44 pin variant, making it hobbyist unfriendly. o It has no on-board crystal support. Thus, either an oscillator or crystal exciter circuit would be needed
Thus, any generic board layout would require RAM, ROM, and the uC
FOr an IEC specific use:
o Technically, you'd only be able to use the 1541 ROMs for those folks who alreayd own a 1541 and remoive the ROM from their 1541 and patch it. Developers like CMD paid a license fee to CBM re-use that code. o You need a 7407 to deal with the need for a HiZ mode on the IO
That said, it's on a napkin here as an idea to try, but I encourage you to work on it.
Jim
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