Dallas/Maxim NVSRAMs used in many test instruments - Page 1
Forum section: electronics / testgear

author: Jwalling
author_rank: Unknown
timestamp: March 28, 2016, 01:31:27 pm
content: It's starting to look like Maxim is the only game left in town for replacement chips used in many different test equipment instruments.Such as the 4mBit DS1250Y used in the TDS700 and TDS7000 series of scopes.Prices have suddenly jumped in the last month or so:http://www.digikey.com/product-search/en/integrated-circuits-ics/memory/2556980?k=NVSRAM&pv142=118&pv154=503&pv276=15&pv276=116&pv276=199&FV=fff40027%2Cfff80434&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=500andhttp://www.mouser.com/Semiconductors/Memory/_/N-488qu?P=1z0w12oZ1yzxfsoZ1z0y15x&Keyword=SRAM&FS=TrueI just bought a DS1250 snap-cap for about $55 less than a month ago. Now it's over $100!TI did have the BQ4015MA-85, but that's not recommended for new designs, so any remaining stock won't be around for long...Worse yet is that the aging Dallas DS1486 used in TDS600 and 700 series of scopes has no direct replacement. They put the RTC in the bottom of memory space where every other chip I've looked at puts it at the top. I suspect that I'll soon need to use a Dremel tool to re-work these with an external battery.As a side note, anyone ever do this surgery on a DS1486?Jay

author: Kjelt
author_rank: Super Contributor
timestamp: March 28, 2016, 02:19:43 pm
content: Alternative would be to use a cheap microcontroller perhaps with some extra needed logic, to emulate such a device.Nice project for someone with the time

author: SeanB
author_rank: Super Contributor
timestamp: March 28, 2016, 03:14:24 pm
content: RS/Farnell/E14 has the snap cap batteries in stock, over 200 at last look. Those at least are not marked as NRFND yet.As to the DS1486, it wqas designed as a direct replacement for a RTC chip, so it would be easy to simply take the base clock chip and add an external SRAM of 4M to it, and the write protect chip, and then simply use a small low power bit of logic to decode the RTC address space ( 32 or 64 bits) from the RAM and map it in as needed. Probably could all fit on a small board a little bigger than the original. The original chiips that make up the dallas parts are probablt still available to do that.

author: Jwalling
author_rank: Unknown
timestamp: March 29, 2016, 01:24:23 pm
content: Quote from: Kjelt on March 28, 2016, 02:19:43 pmAnd the know-how, which leaves me out.

author: nctnico
author_rank: Super Contributor
timestamp: March 29, 2016, 01:26:24 pm
content: If you have a device with an internal RTC then your are out of luck. However the devices which are an SRAM with a battery on top can easely be replaced with an FRAM (on an SMD to DIP converter).

author: Jwalling
author_rank: Unknown
timestamp: March 29, 2016, 01:39:13 pm
content: Quote from: nctnico on March 29, 2016, 01:26:24 pmYep.Quote from: nctnico on March 29, 2016, 01:26:24 pmAre you referring to these?http://www.cypress.com/documentation/datasheets/cy14b104la-cy14b104na-4-mbit-512-k-8256-k-16-nvsramI looked at them yesterday. They would need a voltage regulator for 3.3VDC and an external 68uF cap. Not a big deal, but since the DS1486 cannot be had unless you want to buy from shady Ebay sellers, replacing just one of the NVRAMs in a TDS700 series would be somewhat pointless.Jay

author: stj
author_rank: Super Contributor
timestamp: March 29, 2016, 03:23:55 pm
content: actually, you can use the old RTC combined with sram or fram by using some logic to switch the enable pins based on the address lines.i have a design for a multi-banked fram with the lower 16 bytes shadowed by an old RTC that is fed by a seperate coincell.it only uses 2 74hc series chips to pull it off.

author: TAMHAN
author_rank: Frequent Contributor
timestamp: March 29, 2016, 07:32:22 pm
content: That sounds like a neat project. DallasKillerSeriously, need to talk with some friends. Maybe, just maybe

author: robert_
author_rank: Regular Contributor
timestamp: March 29, 2016, 08:01:40 pm
content: Quote from: Kjelt on March 28, 2016, 02:19:43 pmBear in mind these parallel NVSRAMs are connectd right to the CPU bus and therefore are accessed quite fast. The CPU doesnt wait for your µC which will take well above these 80ns to decode the adress lines, get data from somewhere and output it... Same access timing for the RTC too.You would need some external SRAM which is loaded by the µC upon boot time and shadowed back upon power-down (using an supercap for power hold-up), or parallel FRAM.Updating the RTC values would be tricky as you cant ensure that your writes dont collide with any access from the host system. So you will basically need a dual port sram at least for the RTC registers, which pretty much kills the idea of doing it "simply".So, use a regular SRAM, a little logic to decode wether the ram or the RTC (you should be able to find a RTC chip with the same register set as is used in that module) is accessed, and some battery switchover logic (and an external battery).Maxim still supplies at least some NVRAM controllers with integrated RTC for acceptable prices, so you might be able to find one to replace that module with.

author: Kjelt
author_rank: Super Contributor
timestamp: March 29, 2016, 09:52:51 pm
content: Very good points indeed.

author: mojoe
author_rank: Frequent Contributor
timestamp: March 30, 2016, 02:37:44 am
content: I seem to remember some discussion years ago regarding old test equipment, saying the some of the Dallas chips could be replaced with an EEPROM. I don't recall which ones, and I'm sure it would depend on how the Dallas chip is wired in circuit.

author: bson
author_rank: Unknown
timestamp: March 31, 2016, 07:32:28 am
content: You could create a DIP adapter for an FRAM with SRAM/EPROM compatible pinout. Such as -http://www.mouser.com/ds/2/100/001-86207_FM18W08_256-Kbit_32_K_8_Wide_Voltage_Byt-476756.pdfAbout $13 in SOIC-28 single quantity from Mouser for this particular 32k x 8 unit. 512k x 8 seems hard to find though.

author: Howardlong
author_rank: Super Contributor
timestamp: March 31, 2016, 02:09:37 pm
content: I built a copier/programmer to take the data from a Dallas chip to an FRAM. I couldn't get my "universal" programmer to do this.https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg583511/#msg583511

author: wkb
author_rank: Super Contributor
timestamp: March 31, 2016, 02:21:58 pm
content: Quote from: nctnico on March 29, 2016, 01:26:24 pmOr expose the terminals to the battery on these NVSRAMs and add a new Li coin cell. I used to do this with old Sun hardware that had such RAMs for boot-settings etc. We did not have the money to get new NVSRAMS so this was much cheaper. And it worked just fine.Obviously if the calibration data is in such a chip it can be a bit more tricky, first save the cal data etc before surgery takes place

author: Jwalling
author_rank: Unknown
timestamp: April 01, 2016, 10:56:49 am
content: Quote from: TAMHAN on March 29, 2016, 07:32:22 pmWell, it looks like some folks have some good ideas about how it could be done. I would be willing to pay $100 for working prototypes for the DS1486 and the DS1250, and I could actually test them in a TDS784A that I have to use as a Guinea pig.I know that $100 wouldn't cover the cost, but I think there might be some money to be made as these devices are hitting their 20 year mark. I can't imagine there's much left in them and will start dying everywhere pretty soon! At that point, I'd be a customer as I repair these all the time. I'd pay $100 for a set every time I need one...Jay

author: SeanB
author_rank: Super Contributor
timestamp: April 02, 2016, 05:51:48 pm
content: With the Snaphat devices as well you might run into issues with the supply chain, as they only have a YMM date coding, while you might actually get devices that are over 10 years old, with little indication as to the actual life left.As well some suppliers supply these in a static dissipative packaging, which is definitely not the packaging you want to get a battery of small capacity, with deliberately exposed pins on the underside, and where you are unsure of whether the cell has had a significant portion of it's capacity used up in losses in the package. These little lithium cells are essentially a close to flat discharge curve from new, and are going to show a constant terminal voltage till the last few usable percent of life before dropping off. As discharge current is around a 1M load this is a problem.

author: robert_
author_rank: Regular Contributor
timestamp: April 04, 2016, 03:42:37 pm
content: I did have good success with milling the top off those packages, ripping out the battery and bodging some battery holder on afterwards.Just be careful not to cut into the battery, it will use all of its remaining chemical energy to blow up and make a huge mess...The DS1210 (single digit price) coupled with some standard SRAM could replace the DS1250 and others, though parallel FRAM can indeed work, given the application doesnt constantly overwrite a single cell which might be able to kill FRAM within reasonable timeframes. Things like that happened on HP34970 for example.For those with integrated RTC, the DS1315 seems to be whats inside the DS1243 series and is avialible for mostly acceptable prices.

author: andy2000
author_rank: Frequent Contributor
timestamp: April 05, 2016, 05:02:35 am
content: Quote from: SeanB on April 02, 2016, 05:51:48 pmThat's not a concern because the battery voltage isn't connected to any of the pins. Also, the battery is disconnected until first use, so old stock should last longer than the rated service life if it really is unused.