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'[EE:] RAM for IDE Bus'
2004\06\15@114756 by Matthew Brush

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

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

Any help/info/ideas would be appreciated.

Cheers


=====
MJ Brush
LeftClick.ca Internet Media Services
mbrush@[NOSPAM]leftclick.ca

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2004\06\15@121629 by Matthew Brush

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Thanks for the info.

I don't need to make the bus tri-state since all data
will be latched or not latched into the devices only
when I asked ... right?

Thanks



{Quote hidden}

=====
MJ Brush
LeftClick.ca Internet Media Services
mbrush@[NOSPAM]leftclick.ca

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2004\06\15@122041 by Byron A Jeff

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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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2004\06\15@122250 by Byron A Jeff

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On Tue, Jun 15, 2004 at 12:16:33PM -0400, Matthew Brush wrote:
> Thanks for the info.
>
> I don't need to make the bus tri-state since all data
> will be latched or not latched into the devices only
> when I asked ... right?

Probably. Usually on a RAM the output buffers are only enabled when
CS, OE, and Read are all selected. So it is possible to ground OE and
only use CE to select.

BAJ
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2004\06\15@124326 by Matthew Brush

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> 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?

I'm using 16 bit data base (mostly going from Wesley's
IDE Interface, w/o the 8255 and inverters).  I figured
that since I won't be accessing the IDE drive and the
RAM at the same time, I could share the 16 datalines
and some of the control lines (by holding the IDE in
RESET) to do addressing and data transfers to the RAM.
This won't work?

Cheers


=====
MJ Brush
LeftClick.ca Internet Media Services
mbrush@[NOSPAM]leftclick.ca

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2004\06\15@145549 by Matthew Brush

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These are the RAM chips that I salvaged from an old
video card:

http://www.jameco.com/Jameco/Products/ProdDS/93374.pdf

I was thinking I could put 2 chips' address inputs on
the high byte of the IDE data bus, and then put each
of their 4 IO pins on the low/high 4 bits of the low
byte of the IDE databus.  This way I believe I could
write two chips simultaneously (so 8bits at a time)
and each chip would use the same memory addresses.  I
think this would be pretty easy for reading/writing to
the RAM.

What do you think?


=====
MJ Brush
LeftClick.ca Internet Media Services
mbrush@[NOSPAM]leftclick.ca

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2004\06\15@190135 by Byron A Jeff

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On Tue, Jun 15, 2004 at 02:53:12PM -0400, Matthew Brush wrote:
> These are the RAM chips that I salvaged from an old
> video card:
>
> http://www.jameco.com/Jameco/Products/ProdDS/93374.pdf
>
> I was thinking I could put 2 chips' address inputs on
> the high byte of the IDE data bus, and then put each
> of their 4 IO pins on the low/high 4 bits of the low
> byte of the IDE databus.  This way I believe I could
> write two chips simultaneously (so 8bits at a time)
> and each chip would use the same memory addresses.  I
> think this would be pretty easy for reading/writing to
> the RAM.
>
> What do you think?

DRAM. Much tougher to handle than SRAM. To be honest if you have to ask
the question "What do you think?" then the answer is a firm NO!

Get static RAM. it'll simplify your project tremendously.

BAJ

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2004\06\15@233348 by Matthew Brush
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> Get static RAM. it'll simplify your project
> tremendously.

Bah, I probably don't even need more RAM in this
project.  Speed isn't an issue really, and I'm using a
PIC16F877A putting data on a hard drive either thru
serial or parallel port of a PC.  I just thought it
would be interesting to try, but I don't need any
extra headaches :)  Thanks for the advice.

While were on the topic of RAM, I have a whole pile of
EDO ram from old computers sitting around, any ideas
where I can find the pinouts and/or some interfacing
information?  A brief search on google didn't turn up
much.

Thanks again, Cheers!


=====
MJ Brush
LeftClick.ca Internet Media Services
mbrush@[NOSPAM]leftclick.ca

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2004\06\16@093258 by gmiller

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On Tue, 15 Jun 2004 12:19:40 -0400 Byron A Jeff <spam_OUTbyronTakeThisOuTspamCC.GATECH.EDU> wrote:

>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.

    They're out of stock of that RAM.  I tried to order some a few days ago, they said they'd have more on the 23rd.

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