SRAM with multiplexed bus

Hi all,

Many mainstream microcontrollers have an external multiplexed memory bus.
They all require a latch to connect an SRAM chip. One would expect there
would be a manufacturer who sells SRAMs in 8k or 32kbyte size with a bus
that connects glueless to these micro's but I cannot find such a device. Do
they exist?

Meindert

In article <10p97p7j06kbf68@corp.supernews.com>, 
mhsprang@NOcustomSPAMware.nl says...
> Many mainstream microcontrollers have an external multiplexed memory bus.
> They all require a latch to connect an SRAM chip. One would expect there
> would be a manufacturer who sells SRAMs in 8k or 32kbyte size with a bus
> that connects glueless to these micro's but I cannot find such a device. Do
> they exist?
They used to exist, I remember looking at the specs for a such a beast 
but I haven't seen one for some time.  As I remember they were something 
like twice the price of an SRAM plus separate latch.  I suspect they got 
caught in a price volume conflict (they were too expensive so the volume 
stayed low so they stayed expensive).

The closest I know of now are the Waferscale (now ST) parts with pld, 
SRAM and EPROM/Flash on board.

Robert

Meindert Sprang wrote:
> Hi all,
> 
> Many mainstream microcontrollers have an external multiplexed memory bus.
> They all require a latch to connect an SRAM chip. One would expect there
> would be a manufacturer who sells SRAMs in 8k or 32kbyte size with a bus
> that connects glueless to these micro's but I cannot find such a device. Do
> they exist?

  Good question - there are EPROMs like this, the 27C520 is a modern one,
[64KF in TSSOP20] and Siemens did a small ALE.Sram, but mostly this 
opening has missed the market.
  It's a pity, as there is a pin saving, and a natural expansion by
multiple ALE cycles that exists.
  Closest current chip, is the FRAM from RAMTRON, which (IIRC) latches on
the falling edge of CE, (so that connects to ALE ) - then, you can wire 
that on a PCB minus the HC573.

-jg

> Many mainstream microcontrollers have an external multiplexed memory bus.
> They all require a latch to connect an SRAM chip. One would expect there
> would be a manufacturer who sells SRAMs in 8k or 32kbyte size with a bus

I'm SURE I've seen SRAMs that are "glueless to an 8051". Damn. I wish
I could remember who made them, I think it was Cypress but I can't see
those parts on their site.

Lewin A.R.W. Edwards wrote:
>>Many mainstream microcontrollers have an external multiplexed memory bus.
>>They all require a latch to connect an SRAM chip. One would expect there
>>would be a manufacturer who sells SRAMs in 8k or 32kbyte size with a bus
> 
> 
> I'm SURE I've seen SRAMs that are "glueless to an 8051". Damn. I wish
> I could remember who made them, I think it was Cypress but I can't see
> those parts on their site.

Intel 8155 - AFAIK, already deceased. It was advertised for 8085 and
8088, too.

-- 

Tauno Voipio
tauno voipio (at) iki fi

>  Closest current chip, is the FRAM from RAMTRON, which (IIRC) latches on
>the falling edge of CE, (so that connects to ALE ) - then, you can wire
>that on a PCB minus the HC573.
That's true. But carefully read their datasheet. www.ramtron.com

regards -
Henry

--

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brasilianischer Sauerklee, Natron zum Backen/Baden, u.a.>
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Thanks for all the replies. I am aware of the PSD devices, but I just need
SRAM.
It indeed strange, there *seems* to be a market demand for these types of
SRAM. Heck, some companies are still making 8k x 8 and 32k x 8 chips for
small embedded applications. There must be quite a lot of these applications
using muxed buses.

Meindert

Meindert Sprang wrote:
> Thanks for all the replies. I am aware of the PSD devices, but I just need
> SRAM.
> It indeed strange, there *seems* to be a market demand for these types of
> SRAM. Heck, some companies are still making 8k x 8 and 32k x 8 chips for
> small embedded applications. There must be quite a lot of these applications
> using muxed buses.

  True, but it's also a tough market, and Latched EPROMS are not what 
you'd call at critical mass. They still exist, and in small packages,
( like the 27C520 from Atmel & Winbond ( and Fairchild for a while ) )

  The 27LV1026 is a good example of what CAN be done with smarter-bus
memory.

  Dallas do have a CLK/RAM with 2-4-8K with ALE BUS, but that's not
what would be called a generic part.

  With the growth of DATA Flash, and the drive now to push up the
read bandwidth, multiplexed BUS would be a good solution.

-jg

"Meindert Sprang" <mhsprang@NOcustomSPAMware.nl> skrev i meddelandet
news:10p97p7j06kbf68@corp.supernews.com...
> Hi all,
>
> Many mainstream microcontrollers have an external multiplexed memory bus.
> They all require a latch to connect an SRAM chip. One would expect there
> would be a manufacturer who sells SRAMs in 8k or 32kbyte size with a bus
> that connects glueless to these micro's but I cannot find such a device.
Do
> they exist?
>
> Meindert
>

It is not longer a good idea to use "Many mainstream  microcontrollers"  in
applications requiring
medium sized SRAMs, since the 0,18u and lower embedded flash processes
allows
you to cost effectively integrate 32-64 kB of SRAM.
The AT91SAM7S series will be available in
32kF+8kR,64kF+16kR, 128kF+&#4294967295;32kR, 256kF+64kR etc.
Philips LPC has similar combinations, although the flash size seems to be
fixed to 128kB in most parts.

With low cost ARM toolsets around the corner it is maybe time to to move on
guys :-)

-- 
Best Regards
Ulf at atmel dot com
These comments are intended to be my own opinion and they
may, or may not be shared by my employer, Atmel Sweden.

"Ulf Samuelsson" <ulf@NOSPAMatmel.com> wrote in message
news:2vsp89F2pqsrqU1@uni-berlin.de...
>
> It is not longer a good idea to use "Many mainstream  microcontrollers"
in
> applications requiring
> medium sized SRAMs, since the 0,18u and lower embedded flash processes
> allows
> you to cost effectively integrate 32-64 kB of SRAM.
> The AT91SAM7S series will be available in
> 32kF+8kR,64kF+16kR, 128kF+&#4294967295;32kR, 256kF+64kR etc.
> Philips LPC has similar combinations, although the flash size seems to be
> fixed to 128kB in most parts.

Let me see: my application requires appr. 6000-8000 units/year.
The Mega162 costs me 2.35 euro, the latch appr. 0.10 euro and the SRAM 0,75
euro. That adds up to 3.20 euro. I haven't had an offer for an ARM type
controller for that price yet.

Meindert