Why does the Apple I not use the 6502 PHI2 signal to sync ram writes?

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I se that the replica-1 does use it. Is it because the replica-1 is directly connected to the memory (SRAM) and the Apple I uses buffers on the lines?

Cheers,
Corey

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Re: Why does the Apple I not use the 6502 PHI2 signal to ...

The interface characteristics of the static RAM used on the Replica 1, is vastly different than the DRAM used on the original. I presume that Vince determined that the different timing required gating write with PHI2 in order to comply with the specification of the static RAM he choose to use.

Regards,
MIke Willegal

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Re: Why does the Apple I not use the 6502 PHI2 signal to ...

Thanks,

I was thinking until I can build a "vintage" DRAM memory expansion card I'd grab a 32x8 SRAM chip and hook it up to the Mimeo since the chip is about $2.00 and I have spare 44 pin connectors and PC Boards. I guess it may not be that easy to make a simple card to plug into the expansion connector

Cheers,
Corey

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Re: Why does the Apple I not use the 6502 PHI2 signal to ...

John Calende did a ROM card, a SRAM card would be similar with write capability. I'm not sure if you would need to buffer the data bus or not. Here is the link to the schematics John made.

http://apple1computer.blogspot.com/2010/05/apple-1-basic-firmware-card-it-works.html

Regards,
Mike W.

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Re: Why does the Apple I not use the 6502 PHI2 signal to ...

and as explained in earlier thread the point about the refresh with drams must be kept in mind....

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Re: Why does the Apple I not use the 6502 PHI2 signal to ...

Yep understood about DRAMS. But I think the Apple-1 has enough refresh time for that. This issue with the "Vintage" DRAM card on the Apple-1 is vintage RAMs require 3 different voltages. The Apple I only provides +5v regulated to the expansion connector all the other voltages are un-regulated. So a "card" memory expansion isn't as easy as a modern SRAM chip to hook up to the expansion connector. I am going to build the "vintage" DRAM card but I'm in the middle of about 3-4 different projects now and can't spend the time yet to design and build it. I figured the SRAM would be a very quick "hack" for some temporary memory until I can design the DRAM card. I really want to play the "Wendell Sander" version of Star Trek on my Mimeo but it needs more RAM Smile

Cheers,
Corey