[sdiy] SRAM versus DRAM

[Scott Nordlund]

There's no real need to mess around with "vintage" RAM chips- They were chosen on a basis of necessity rather than any specific design advantages.  A lot of them are very obscure now, use multiple power supply voltages, high power consumption, etc...

With a larger chip (512k x 8?), you'll be able to make much longer delays (at a reasonable sample rate), and you can also split the memory into multiple "banks" that can be switched from external signals (I've had a lot of fun with this recently).

SRAM is probably a better option since the interface is simpler.  It can also be battery backed in case you want to make some sort of primitive sampler.

Use something with a bidirectional data bus.  Chips with separate input/output pins will probably still need latches or something, so it won't complicate things very much.

If you want 1 bit wide DRAM, you can probably get more than you can choke on from an old 286 motherboard or ISA RAM expansion card.  I wouldn't really recommend going that way, though.

----------------------------------------
> From: subjectivity at hotmail.com
> To: jluciani at gmail.com
> Subject: RE: [sdiy] SRAM versus DRAM
> Date: Wed, 24 Jun 2009 01:24:55 +0000
> CC: synth-diy at dropmix.xs4all.nl
>
>
> i know a lot of digital delays use the 2164 DRAM (peavey, electro harmonix and MXR digital delay)
> which is why before I saw the polyphony digital delay project which calls for SRAM (4k x 1 bit, 8 of them) I had thought DRAM was the way to go in a digital delay.
>
> sadly the more i look into this the more I am seeing that there is a real issue...
> if you want seperate In and out pins (which seems to make things a lot easier) than you need to use really small RAM chips and Use
> 8 of them for an 8 bit DAC which is a lot of chips.
>
> BUT if you want to use something that puts out 8 bits, you need to figure out the logic for properly switching between In and Outs
>
>
> it sure would be fun to figure this out though!
>
> thanks all
>
>
>
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> ----------------------------------------
>> Date: Tue, 23 Jun 2009 21:19:11 -0400
>> Subject: Re: [sdiy] SRAM versus DRAM
>> From: jluciani at gmail.com
>> To: subjectivity at hotmail.com
>> CC: synth-diy at dropmix.xs4all.nl
>>
>> On Tue, Jun 23, 2009 at 8:15 PM, Dan Snazelle wrote:
>>>
>>>
>>> in a project that calls for SRAM can you use DRAM instead?
>>>
>>> I know they are fundamentally different in that one type has to be refreshed but i suppose i do not understand
>>> WHY the refresh is important
>>>
>>> in the case of a digital delay for example
>>
>> IIRC the DRAM refresh rates are on the order of micro-seconds not the
>> many milliseconds
>> you would need in a digital delay.
>>
>> A number of uC's have DRAM refresh circuitry that automatically does
>> the refresh for
>> you. I worked with a Coldfire chip that did.
>>
>> (* jcl *)
>>
>> --
>>
>> You can't create open hardware with closed EDA tools.
>>
>> http://www.luciani.org
>
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