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PostPosted: Fri Jan 27, 2006 6:36 pm 
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Joined: Tue Mar 02, 2004 8:55 am
Posts: 996
Location: Berkshire, UK
... I can't use an 8 pin PIC 12F629 to generate a 1MHz clock input, /RES and /NMI signals for a R6502-P?

I don't have any low speed crystals or logic to build an oscilator but I do have a stack of PICS.

I was planning on using the internal 4Mhz oscilator with one pin set to output FOSC/4 for phi0. I want to have two switch inputs (for reset and debug) debounced in software and which connect thru to output pins for /RES and /NMI.

That leaves me one pin to control a LED to show that its powered up.

Would it work?

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PostPosted: Fri Jan 27, 2006 8:41 pm 
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Location: Southern California
That would work, but the internal RC oscillator on the PIC won't be super accurate. If the 6502 were a CMOS one, you could just put an RC on its clock pins, as well as on the reset input since it's a Schmitt-trigger input; but using the PIC to integrate the functions might still save some board space, in addition to giving the other features you want.


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PostPosted: Sat Jan 28, 2006 8:30 pm 
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Joined: Sat Jan 04, 2003 10:03 pm
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I'm actually planning on using an internal RC-clocked ATmega8 as the Kestrel's bus arbitration logic chip. Yeah, it'll take about a microsecond or two to actually grant a peripheral access to the bus, but it'll work (well, it SHOULD at least), and it'll be compact enough that I don't have to invest in FPGA or CPLD technology. Speaking of which, I'm finally coming close to the expansion connector layout that I'm happy with. When I'm done, I'm going to post the details here. I'm borrowing many techniques from various sources, ranging from Apple II's expansion connectors to NuBus and PCI. :)


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