On Tue, Jun 15, 2004 at 11:47:41AM -0400, Matthew Brush wrote:
> Hello all
>
> I'm working on a PIC16F877 IDE hard drive interface
> and I was wondering if someone could suggest a good
> type of parallel RAM that I could put right on the IDE
> bus to hold the next 512 bytes of info that I'm
> reading/writing to the hard drive.

Probably some type of static RAM.

>  I've never used
> parallel ram before, but I think this should work
> right?

It depends. You have to be able to address the ram to do
the job.

>
> I have 2 or 3 spare pins on the F877 so I would be
> able to control the CS pin of the ram or whatever it
> uses.

But agaon what about the addresses? Since it's a sequential interface
you may be able to get away with using some counters (like a pair of 74HCT393
ripple counters) to address the memory. Are you using an 8 line IDE data bus
or 16?

>  What about pulling some RAM from an oldschool
> video card (it's in sockets)?

That's probably DRAM which you want to stay away from. What would really
work well is old 386/486 cache ram, which was 20-25ns static RAM. A one
minute look around Jameco.com resulted in this part: 242376cl. A 32kx8
35ns cache ram for $2 USD. It can hold 64 sectors worth of data.

With only 3 pins left you may need an intermediate control chip. Since you'll
only need outputs, because the data bus will share the bus with the IDE,
Maybe a 74HC595 may work giving you 8/16/24 outputs for the cost of 3 PIC I/O.

BAJ

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