Reverse engineer Dallas DS1742W?

[friendtogeoff]

Wow, really nice piece of work @sicco.

I'm interested in getting one of these to put into a TDS3054 (not B or C) as an alternative to buying a TDS3EM from the sharks. Any hints on where to find the eBay offer?

[sicco]

I have two that are fully populated and tested, as per picture.
Looks like my eBay ad for them from ~November has disappeared, but happy to sell and ship directly to you.

150 EUR for one, plus 20 EUR shipping to a UK address. Not sure what customs duty get added for you post Brexit, but obviously that for you to settle.
Paypal should work, IBAN maybe even better.

Share your shipping address etc via direct message please (instead of full forum post).

Warm regards, Sicco.

 

[sicco]

PS just noticed that on the picture I just made, there was a board plugged in that does not have Ethernet (TDS3EM emulation), but the two units in front of the scope will give you Ethernet as in:

[cuebus]

Hi all,

I decided to definitively figure out how these DS1742Ws are constructed so I softened the epoxy on the one I desoldered from my scope and got to work.

Turns out, unlike the DS1486 that I reverse engineered last year, this one uses a single chip solution. Both the RTC and RAM are on the same die. This part is a TSOP-1 32 pin part marked Dallas DS1743E-3 (the 3 is the voltage designator, there is also a DS1743E-5 for 5V chips). As you can expect it's the same part used in the DS1743W, which is 8 x 8k, just 2 address pins are unused, similar to james_s' adapter board solution.
Battery used is smaller- just a BR1225 coming in at 48mAh. One may think this is an issue but I measured the current draw in data retention mode to be only 300nA, giving it a lifetime of 18 years unpowered.
My scope is from 2000 and has 50,000 hours on it, so not counting self discharge, my original chip would have had a life of about 4 years left still unpowered.

Pinout of the TSOP is close but not the same as JEDEC standard since naturally there need to be some pins there for the RTC xtal and battery inputs. 

If you can acquire a DS1743WP PowerCap (some available on eBay), you can do what I did and remove that chip (it's the same one) and solder it onto a PCB made to copy the DS1743W layout. I attached the gerbers of the layout I made.
The chip on the powercap is tacked with adhesive on 4 edges, but they are right on the edge of the chip so can be relatively easily cut away with a knife. As long as you get most of it off you'll have no issue removing the chip.

You only need 2 other parts, a crystal, and a battery.
I used the same crystal as for my DS1486 project, CMR200T32768DZBT
I don't know the load capacitance required by this one but I've had it running several days in my scope now and it's still exactly on spec with another clock.
Battery for my board is BR-1225/H1AN. As stated, you'll get 18 years minimum use with this.

Altogether it makes for a nice compact replica, and fits like a glove.

Cheers,
Robin

[james_s]

Well that fits what I could see in the xray picture of mine. Interesting that the IC is a DS1743.

[zebity]

Hi James_s and others,

happy to report that this nut has been cracked, not once but twice, by SGI community.

see this post on IRIX Network for drop in replacement by cz7asm with working clock and nvram:

https://forums.irixnet.org/thread-3360.html

And these post on SGI User Group:

By cz7asm: https://forums.sgi.sh/index.php?threads/ds1742-nvram-chip-replacement.702/

And Glitchworks prototype: https://forums.sgi.sh/index.php?threads/dallas-ds1742w-replacement.707/

I read the cuebus post, but it is not clear to me if this provides both RTC and NVRAM solution. If so then that gives three replacement options…

I have personally tested the cz7asm version, in SGI O350 (I am jwhat on IRIX Network) and confirmed it works like a charm. It has also been verified in SGI Fuel.

I have no affiliation with either cz7asm or Glitchworks, I am just another person who was doing drilling and investigation to see if a replacement solution could be found.

It would be good to know if the replacement options also worked in other equipment.

Cheers from Oz,

zebity (jwhat/John)

[cz7asm]

Hi, if anyone is interested I have the DS1742W replacement available on ebay - https://www.ebay.com/itm/284766293220

Thank you zebity/John for spreading the word.

[james_s]

Looks good. I'm curious, what IC did you base it on? Did you have to find a source of Dallas custom ICs or did you come up with a modern solution using current production parts?

[zebity]

Hi James_s,

looking at it, it looks like it is DS1558D based,

So I presume to get this to behave the same as DS1742 you just have to hold the lower of the additional address lines (A0-A8 ?) high to make sure the RTC Clock addressing is mapped correctly.

As DS1742 has A0 - A10 and DS1558D has A0-A18 (so additional 8 address lines).

So not serial to parallel conversion.

Cheers from Oz,

zebity

[Dave Wise]

Marked "DS1558D" is DS1558W which is 3.3V.  Its additional address lines are A11-A18.  It has eight extra registers you want to avoid, at 7FFF0-7FFF7.  Hold A11-A18 high except tie at least one to A3 so xx8-xxF hit the top bank while xx0-xx7 go elsewhere.  BF (Battery Flag) is not defined, but I don't think Tek cares.  Everything else is compatible AFAICT.

I will certainly want one sometime for my TDS3054B which retains data but the clock stops.

[Dave Wise]

And... GlitchWorks has developed the GW-1742W-1.  He's selling it at https://www.tindie.com/products/glitchwrks/glitch-works-gw-1742w-1-dallas-ds1742w-replacement/ .  He's willing to program parts but he doesn't know the TDS3000 format, we'll have to send a dump.

I have a Needhams EMP-300 programmer.  I suspect I can read a DS1742W by calling it a 2716 eprom.

[Dave Wise]

GlitchWorks GW-1742W-1 was out of stock, now available again on Tindie.  I'll reserve one but I'm not ready, I'm using the scope and don't want to take it down.

GW warned me off treating as 2716 EPROM:

**DO NOT** attempt to read the original as a 2716! You may inadvertently apply programming voltage which will fry the 1742W!
You can safely read this part as a DS1220 NVRAM. If your current programmer doesn't support that, the cheap option is to get a TL866 or one of the newer revisions. We've successfully tested with that programmer in-shop to confirm compatibility for a customer.

Since my EMP-300 supports DS1220, that's what I'll set it for when I read my DS1742W.

[james_s]

You can read them easily enough but writing them is where problems tend to crop up. I forget exactly what I ran into but I ended up wiring up some switches and LEDs (actually I used a FPGA dev board but only because I happened to have one) and manually programmed the needed bytes and configuration bits by hand.

[bschwand]

We know exactly what's inside these, the PowerCap version is not potted. There is an off the shelf SRAM, a battery, a 32kHz crystal, and a Dallas ASIC which is a RTC and battery backup controller. Due to the custom chip it doesn't really help you to know what's in there although you can cut the old battery out and solder in a new one.

While the DS1742W is discontinued, the DS1744WP is in active production and I made an adapter using those to replace the DS1742W in Tek TDS3000 scopes. You can build one yourself if you like, aside from mechanical fitment constraints it will work in any application designed for the DS1742W, and the PowerCap package it uses has a replaceable battery.
https://github.com/james10952001/DS1744WP-to-DS1742W-adapter

Is it possible to directly use that module in a Tek3034B or does it have to be programmed first ?

[YetAnotherTechie]

On "B" models you will need to write the MAC address back on the ram, or the network will not work.

[bschwand]

ok, is there an nvram dump for the 3034B available somewhere, I am searching the forums and have not found anything so far, just that the MAC is somewhere in the beginning of the nvram.