SRAM/latch recommendation

Go To Last Post
6 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I need to add a 64KB SRAM chip and associated latch to a 16 MHz ATMega design (haven't settled on the actual CPU yet but probably an ATMega64). Can anybody recommend a specific SRAM/latch combination that will run with no wait states? I'm happy to use a larger part, if necessary. Thanks.

Karl

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The following parts can be ordered from Digikey:

128K x 8 15ns SRAM (428-1004-ND), $3.89
SN74AHC573DW Latch (296-4612-5-ND), $0.48

These are both surface mount packages.

Dave

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks, Dave. I haven't worked through the timing diagrams yet, but have you actually used this combination at 16 MHz w/ no wait states?

Karl

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

lautman wrote:
I haven't worked through the timing diagrams yet, but have you actually used this combination at 16 MHz w/ no wait states?

Yes I have on multiple boards. However, this was for a home project where I have control over the operating conditions. Looking at the datasheet, the toughest parameter is the Read Low to Data Valid, which is specified as the clock period minus 50nS. So the timing actually is short by about 2.5ns for the 15ns SRAM. There are faster SRAM chips available but they're harder to get and a LOT more expensive. Is this for a home project or commercial project?

Dave

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Digikey has 340 of the CY7C1019CV33-12VC (12 ns read cycle) in stock for only $3.96 ea. These are pin/function campatible with the CY7C1019BV33. I actually have a couple. This is a comercial project, so I need to go by the book. Unfortunately, it's the only SMD in the design so far, (the 74AHC573 is also available as a DIP, btw; if there's something special about the SMD I should know, do tell; unfortunately, I have some 'HCs on hand but no 'AHCs), and I'm only making one system, so I'll be soldering by hand. Haven't had to solder enough SMDs yet to be any good at it. Any tips? ;-P

Karl

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

lautman wrote:
Digikey has 340 of the CY7C1019CV33-12VC (12 ns read cycle) in stock for only $3.96 ea.

That's a nice price but keep in mind that it is also a 3.3V part. You talked about running at 16MHz so I was only looking at 5V parts.

lautman wrote:
Unfortunately, it's the only SMD in the design so far

You mentioned the Mega64 - that's only available in SMD too.

lautman wrote:
I'll be soldering by hand. Haven't had to solder enough SMDs yet to be any good at it. Any tips?

There's nothing magic about SMD - I do it at home all the time. First step is to read the article by Colin O'Flynn on the home page of this site (Low Cost SMD Soldering Guide). That should get you going.

Dave