Static RAM requires simply that you apply address, control, and, if necessary,
data, and, so long as power is applied, the content remains stabile. Dynamic
RAM's rely on stored charge that gradually leaks off, and, therefore, must be
refreshed. On DRAMs like 4116's, this occurs when the nRAS strobe is raised at
the end of a row access. This writes the charge back to all the cells in that
row. Consequently, the length of the RAS precharge cycle is just as long, or
nearly so, as a read access cycle, as the data is written back to all the cells
in the row from the row buffers. The advantage of the DRAM is that it requires
much less silicon per bit, for a given geometry, so costs less (less silicon at
$XX/lb) per bit. The disadvantage is that, in the case of all the 16-pin
multiplexed address DRAMs, more logic and somewhat critical signal timing was
required. Later DRAMs followed the same general approach, though it's gotten
quite a bit more setup intensive in recent years.
Dick
----- Original Message -----
From: "Louis Schulman" <louiss_at_gate.net>
To: <classiccmp_at_classiccmp.org>; "Tony Duell" <ard_at_p850ug1.demon.co.uk>
Sent: Friday, July 06, 2001 7:04 PM
Subject: Re: 2116 and other old memory chips
> On Sat, 7 Jul 2001 01:11:11 +0100 (BST), Tony Duell wrote:
>
> #>
> #> I am in the process of attempting to repair, with Pete Turnbull's
> #> invaluable guidance, an Exidy Sorcerer.
> #>
> #> The manual recites that the memory chips, depending on
> configuration,
> #> are 2104 (4k) or 2116 (16k).
> #>
> #> A casual perusal of chip sources shows that most begin their dynamic
> #> ram sections with 4116 chips. The only mention I have found of 2116
> #> chips is in a reference to the original IMSAI memory board.
> #>
> #> So, my questions are: Are 2116 chips 3-rail? Are 4116 chips
> #
> #As far as I can see, yes the 2116s are 3-rail and have the same
> pinouts
> #as 4116s. A lot of the time, various manufacturers made very similar
> RAM
> #chips with slightly different numbers (another example is the 2016
> 2K*8
> #SRAM which is very similar to the 6116). Sometimes there were slight
> #timing differences between various manufacturer's chips, often it
> doesn't
> #matter.
> #
> #I would be very suprised if the Sorceror doesn't work with 4116 DRAMs
> in it.
> #
> #> equivalent? Does anyone have a source for 2116 chips, if they are
> not
> #> equivalent? What about 2114 static ram (used in the video section
> of
> #> the Exidy)? Same problems? Were they all three rail?
> #
> #The 2114 SRAM is single-supply rail (+5V only). Again, it was made by
> #several companies (but I think most of the time it was called the
> 2114).
> #It also happens to be the chip I've had the most failures from :-)
> #
> #>
> #> A general lecture on the nature of old memory chips and their use
> and
> #> selection would be very helpful (hint to Tony Duell).
> #
> #Most of the time, RAMs are pretty generic. Match up the capacity, type
>
> #(SRAM or DRAM) and number of pins, and you're close to finding a match
> :-)
> #
> #In general, SRAMs were single-rail, +5V only. DRAMs were often 3-rail
> up
> #to and including the 16K bit parts. There were single-rail 16Kbit
> DRAMs,
> #but they are not that common, and they came out later than the 3 rail
> parts.
> #
> #Most DRAMs have a multiplexed address bus (that's how you fit a 16K
> RAM,
> #needing at least 14 address lines, 1 data line, 1 write enable line
> ,and
> #3 power lines into a 16 pin package). You send the address in 2 parts
> and
> #bring RAS/ and CAS/ low as appropriate. Some older 4K DRAMs, in 22 pin
>
> #packages, have a normal address bus with 12 separate pins. Those 22
> pin
> #DRAMs are odd in othter ways, like needing a strobe pulse at 12V
> levels.
> #
> #I am not sure exactly what you want to know, though. If you can say
> what
> #information you need, I'll try and dig out the databooks.
> #
> #-tony
> This answers most of my questions, thanks. One further question. What
> is the difference between "static" ram and "dynamic" ram, since both
> are "volatile" ram? Or, putting it another way, what is "static" about
> "static" ram, since it changes as well?
>
> Louis
>
>
Received on Fri Jul 06 2001 - 20:24:09 BST