Forums

SRAM with multiplexed bus

Started by Meindert Sprang November 12, 2004
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 -- <Schau auch mal auf meine Homepage www.ehydra.dyndns.info> <u.a. Versand von Wasserflohzuchtansatz, Wasserpflanzen/-schnecken, brasilianischer Sauerklee, Natron zum Backen/Baden, u.a.> <Alternativ &#2013266172;ber http://people.freenet.de/algenkocher>
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+&#2013266100;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+&#2013266100;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