Looking for RAM. - Page 1
Forum section: electronics / beginners

author: HardBoot
author_rank: Regular Contributor
timestamp: August 25, 2012, 09:42:57 pm
content: I'm looking for dip ram chips which are as simple as sram to use but with bigger capacities, I need something in the 16-64MB range.Basically for bufferring data for a micro because micros have tiny amounts of integrated ram, so it needs to be pretty quick, 100+MBps range.If there's nothing dip, anything socketable like plcc would be just fine.If all else fails... is there dip/plcc/anythingsocketable DRAM?

author: T4P
author_rank: Super Contributor
timestamp: August 26, 2012, 04:37:36 am
content: Well basically with all the inductance of a through hole package sadly i don't think you can do 100MBPSAnd bad news for ya, it's all surface mount

author: IanB
author_rank: Super Contributor
timestamp: August 26, 2012, 05:19:23 am
content: Quote from: HardBoot on August 25, 2012, 09:42:57 pmI'm a bit puzzled by how general and unspecific your question is.When you say "micro", do you mean microprocessor or microcontroller?Is 100 MBps 100 megabytes, or 100 megabits?If we assume megabytes, and 8 bit bytes with an 8 bit data bus then you would need 100 million memory access cycles per second and therefore a CPU clock speed of at least that. Using 16 bit wide or 32 bit wide data buses could reduce that requirement.Have you looked at data sheets and application notes for the particular hardware you are interested in? There is often specific and detailed information available there.

author: amyk
author_rank: Super Contributor
timestamp: August 26, 2012, 09:16:17 am
content: DIP SRAM is not going to be very high capacity, hundreds of KB at most. 256Kx8 and 512Kx8 sizes were common in motherboards 2 decades ago for cache.If you want cheap fast memory, use DDR DRAM.

author: HardBoot
author_rank: Regular Contributor
timestamp: August 26, 2012, 02:22:48 pm
content: Quote from: T4P on August 26, 2012, 04:37:36 amDip isn't too bad electrically... lots of digital and analogue chips running at a few hundred MHz, when you have long wiggly traces with vias, do you think the package it soo much worse compared to... sop16?Quote from: IanB on August 26, 2012, 05:19:23 amDual PICs sharing 1 memory bank which has data streamed into it by a CPLD which would be the data multiplexer for the chips. 100MBps is higher than what I need, <80MBps.Quote from: amyk on August 26, 2012, 09:16:17 amUsing DRAM is a pain, and I don't have a ton of spare logic, it's annoying enough with FPGA... years ago I remember seeing 8 and 16MB ram chips in plcc, all discontinued.Aren't there dram chips with built in logic to make them act like sram? I swear I've come across something like that.

author: SeanB
author_rank: Super Contributor
timestamp: August 26, 2012, 02:55:11 pm
content: If the data rate is high enough, and you can guarantee that you will hit all the addresses in a row or column in less than the max refresh interval then you do not need a dedicated refresh controller. The act of reading a row refreshes all the other rows in the chip for that read/write cycle, and if you do more than 256 incremental reads no need for refresh.

author: codeboy2k
author_rank: Super Contributor
timestamp: September 03, 2012, 01:53:57 am
content: Quote from: SeanB on August 26, 2012, 02:55:11 pmIn the old days I just wrote an interrupt routine that sequentially scanned memory at the refresh rate. That's all that was needed.Not the most efficient, but it worked and was simple. The hardware we built at the time was very discrete, did not have anymemory controller on the MCU, or on the board at all, and we used rows and rows of small DRAMS on 18-20 pin DIPS I thinkit was.This was around 1986-87.By the way, if you need this for a one off project, you can get some 30-pin 16MB SIMM modules on eBay, like the picture. just find something fast enough and make the data bus wide enough for your speeds.

author: Monkeh
author_rank: Super Contributor
timestamp: September 03, 2012, 02:10:46 am
content: Quote from: codeboy2k on September 03, 2012, 01:53:57 amDie. That is all.

author: IanB
author_rank: Super Contributor
timestamp: September 03, 2012, 02:27:11 am
content: Real computers use memory measured in MB (or was it KB?). It's only these new-fangled toy computers that need GB of memory installed before they will even boot up to a blank screen.

author: SeanB
author_rank: Super Contributor
timestamp: September 03, 2012, 04:58:34 am
content: I worked on one that had memory measured in bytes, and it used core planes as well. There was an upgrade that used a 6116 and a battery for backup.

author: andersm
author_rank: Super Contributor
timestamp: September 03, 2012, 12:21:19 pm
content: Quote from: HardBoot on August 26, 2012, 02:22:48 pmPseudo-SRAM is available from at leastISSI,WinbondandFujitsu. I say available but... Any type of memory with any kind of density will also be available in BGA or TSSOP only, with x16 or x32 bus width.

author: codeboy2k
author_rank: Super Contributor
timestamp: September 03, 2012, 08:07:19 pm
content: Quote from: Monkeh on September 03, 2012, 02:10:46 amI missed the jokeAre you saying SIMM modules have a tendency to die? Or are you wishing me to expire herelol

author: Monkeh
author_rank: Super Contributor
timestamp: September 03, 2012, 08:16:53 pm
content: Quote from: codeboy2k on September 03, 2012, 08:07:19 pm'Single In-line Memory Modules modules' is what you've just said. Twice.

author: hlavac
author_rank: Frequent Contributor
timestamp: September 04, 2012, 12:00:28 pm
content: Sounds complex...To serve as a buffer for 80 megabytes per second you will need 80M writes and 80M reads per second,you would have to use like 10 55ns SRAM chips in parallel and read/write the data in 10byte chunks at 16Mops...80 data lines, you could maybe share the address lines with some line buffers

author: codeboy2k
author_rank: Super Contributor
timestamp: September 04, 2012, 08:21:22 pm
content: Quote from: Monkeh on September 03, 2012, 08:16:53 pmaha.. I see it got your shorts in a knot. Sorry about that.That must hurt as much as DIP package, or BJT transistor

author: Monkeh
author_rank: Super Contributor
timestamp: September 04, 2012, 08:42:46 pm
content: Quote from: codeboy2k on September 04, 2012, 08:21:22 pmQuite. Illiteracy is a sin.