Author Topic: EEVblog #615 - Prema 6047 Multimeter Followup  (Read 21435 times)

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Offline EEVblog

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EEVblog #615 - Prema 6047 Multimeter Followup
« on: May 11, 2014, 07:33:13 am »
Dave checks the Dallas DS1220Y chip in the Prema 6047 7.5 digit multimeter to see if the battery is dead, and if the calibration constants have been lost.
http://datasheets.maximintegrated.com/en/ds/DS1220Y.pdf
ROM is here:
http://www.eevblog.com/files/Prema6047-ROM-8-5-91.BIN

 

Offline Chipguy

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #1 on: May 11, 2014, 08:30:09 am »
You might consider to whack in an FRAM as a replacement for the DALLAS ZeroPower NV-SRAM
They are available as 8Kx8 versions, like the 6164 SRAMs in JEDEC standard SOIC chip.

The only thing you need is one of those little adapter PCBs for 2K DIL sockets.
Should be available from ebay for a few bucks. I couldn't find one with a quick search right now.

FRAM (former Ramtron, now Cypress) datasheet:
http://www.cypress.com/?rID=76573
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Offline Switching Power

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #2 on: May 11, 2014, 08:42:28 am »
You are lucky that the DS1220 was still good.

At my work we once had a dead delay generator that used a Dallas DS5000 microcontroller that uses battery backup NVRAM for the main firmware :palm:
So after al those years being in storage the battery was dead and the firmware got corrupted in such a way that the generator was doing random crap.

Lucky after a week of mailing some big research laboratory's we got the original HEX file to restore it in a brand new DS5000 and got the delay generator working again :)
 

Online Dr. Frank

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #3 on: May 11, 2014, 09:39:04 am »
The DALLAS DS1220Y is the same one used in the 3458A.

'quarks' also had a 1989 vintage NVRAM in his instrument, and mine was 14 years old, both still working.
But other 3458A owners reported data loss after 10 years already.

So you should get a new NVRAM.
 
We have copied the contents of our NVRAMs to fresh ones, they are still available from maxim, or from mouser for a low price.
The new designation is: DS1220AD-150+, around 8$.

As you already have saved the content and are able to write it back, you could check, if the NVRAM actually contains the default calibration constants only.
Maybe somebody before experimented with the loading process, or there had been a checksum error before, and the instrument loaded the default values by itself.

Anyhow, this instrument needs a fresh calibration, so I look forward to a calibration video.

Frank 
 

Offline justanothercanuck

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #4 on: May 11, 2014, 01:17:55 pm »
Wouldn't it make more sense to store the constants in the ROM?  I'd hate to own one of these, and pull it out of the closet to find out that it bricked itself.  (Not that it stopped other manufacturers from doing the whole suicide battery thing...  I'm looking at you Capcom.)
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Offline EEVblog

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #5 on: May 11, 2014, 01:35:21 pm »
Wouldn't it make more sense to store the constants in the ROM?

Not from a point of view of the calibration house. That would be a real pain to have an EPROM programmer and and procedure on how to program the data in. No cal lab would want to do that. Front panel and NVRAM is the way to go.
The Prema has some sort of factory calibration built into ROM. Whether that is measured data per unit, or just default values that will get close enough, I don't know.
 

Offline Rasz

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #6 on: May 11, 2014, 02:15:04 pm »
http://www.eevblog.com/files/Prema6047-ROM-8-5-91.BIN

not a firmware (at least the primary one)
all it appears to do is count to fff8 (delay?) and jump to $8035

Code: [Select]
loc_0:                             
                CLD
loc_1:                             
                LDA     #$FF
loc_3:                             
                STA     $0003
                LDA     #$F8 
                STA     $0002
                LDA     #$C1
                STA     $0001
                LDA     #0
                STA     $0000
                LDA     #0
                STA     $0004
                TAY
loc_16:                             
                CLC
                LDA     $0000,Y
                ADC     $0004
                STA     $0004
                INC     $0000
                BNE     loc_23
                INC     $0001
loc_23:                             
                LDA     $0001
                CMP     $0003
                BNE     loc_16
                LDA     $0000
                CMP     $0002
                BNE     loc_16
                LDA     $0004
                STA     $FFF9
                NOP
                JMP     $8035

can test code at http://skilldrick.github.io/easy6502
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Offline free_electron

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #7 on: May 11, 2014, 02:26:11 pm »
A little tidbit : dallas did NOT invent those battery backed rams. It was actually a Mostek idea , later borged by ST. The 48z02 is a mostek partnumber. St still produces these in the snaphat family.
Dallas modded the idea (went around the patent) by encapsulating the batteries.
The mostek did have removable batteries 237 type like used in hp calculators. The chip had a lid with two screws. Later on st modded the body and made the battery pack removable.

Why not use a cell next to the ram ?
First you need special extreme low power rams. Often there is more leakage on the pcb due to greasy fingerprints and badly washed boards (flux remnants) than what the ram consumes
Second .. Wave soldering batteries is not a good idea. Connectors neither ...
Third. Most engineers in the early days couldnt design a proper write lock circuit that would protect the ram contents during brownouts or powercycles

These chips solve that. They have on board power monitors that cut the write gate. Some of them have an expiration mechanism. You need to write a sequence to a specific address (this doesnt alter the data stored there) to unlock for write. You can then write 2 or four bytes. After which the device relocks writing. There are other mechanisms as well in the really advanced ones. Time lockout, number of writes lockout and more.

Dallas then started adding realtime clocks and st followed .

Now, as far as longevity goes this is a different story.
These devices come out of the factory with the battery disengaged. It is not until you activate them by writing successfully the first time that the battery connects internally. In this deepfreeze mode the shelf life is like 20 years and then they still guarantee another 10 years operational life after that.

For some devices they actually released the sequence to put the device back in freeze mode . Data is lost of course.
« Last Edit: May 11, 2014, 02:38:51 pm by free_electron »
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Offline edpalmer42

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #8 on: May 11, 2014, 03:35:13 pm »
Dave,

It looked like there wasn't much epoxy over the battery on the bottom of the Dallas chip.  Depending on whether the exposed side is positive or negative (it looked like it was the positive side) it shouldn't be difficult to drill a small hole by hand to allow you to probe the battery and measure the voltage.  Granted, you can't tell how close the memory is to failing, but it would still be useful information.  I recently did this with a DS1230Y with a 0030 date code and found the battery is still at 3V32.

Another interesting experiment would be to install the 6116 chip, restore the original cal constants and see how much the meter has drifted since it left the factory.

There's one thing I didn't understand in the video.  You talked about the possibility of the unit writing and then reading the NVRAM during the power-on tests.  Since the write line is held high by the keylock, how could it write to the NVRAM?  I would expect that the checksum would be written to the memory during the calibration process and then checked on powerup to ensure that the cal constants were valid.  Am I missing something?

Ed
 

Offline Rutger

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #9 on: May 11, 2014, 04:17:48 pm »
You talked about the possibility of the unit writing and then reading the NVRAM during the power-on tests.  Since the write line is held high by the keylock, how could it write to the NVRAM?  I would expect that the checksum would be written to the memory during the calibration process and then checked on powerup to ensure that the cal constants were valid.  Am I missing something?

The checksum can only be read during powerup and will be compared to a value stored in the ROM. There is no writing to the NVRAM, if Dave said so he is wrong.
 

Offline SeanB

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #10 on: May 11, 2014, 04:45:44 pm »
Looks like the SRAM data is good, just most likely the reference has finally finished aging after 20 years of doing so. If calibrated now I would guess it will stay stable for a long time, though it probably would be best to just leave it on for a week to see if there is any long term drift.
 

Offline NiHaoMike

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #11 on: May 11, 2014, 06:00:24 pm »
Might it be possible to replace the battery RAM with an EEPROM?
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Offline Chipguy

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #12 on: May 11, 2014, 06:10:31 pm »
Might it be possible to replace the battery RAM with an EEPROM?

Seems you have not read the entire threat  :=\
An EEPROM will not work because it needs waiting time after each write, the software would have to be modified   :scared:
An FRAM will work though, since it is a RAM with EEPROM features. Data retention time 151 years  :-+

Here my original post:
Dave might consider to whack in an FRAM as a replacement for the DALLAS ZeroPower NV-SRAM
They are available as 8Kx8 versions, like the 6164 SRAMs in JEDEC standard SOIC chip.

The only thing you need is one of those little adapter PCBs for 2K DIL sockets.
Should be available from ebay for a few bucks. I couldn't find one with a quick search right now.

FRAM (former Ramtron, now Cypress) datasheet:
http://www.cypress.com/?rID=76573
Modify message
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Online David Hess

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #13 on: May 11, 2014, 06:15:09 pm »
A little tidbit : dallas did NOT invent those battery backed rams. It was actually a Mostek idea , later borged by ST. The 48z02 is a mostek partnumber. St still produces these in the snaphat family.
Dallas modded the idea (went around the patent) by encapsulating the batteries.
The mostek did have removable batteries 237 type like used in hp calculators. The chip had a lid with two screws. Later on st modded the body and made the battery pack removable.

Later Dallas had versions with removable battery packs as well so wave soldering could be used.

Quote
Why not use a cell next to the ram ?
First you need special extreme low power rams. Often there is more leakage on the pcb due to greasy fingerprints and badly washed boards (flux remnants) than what the ram consumes
Second .. Wave soldering batteries is not a good idea. Connectors neither ...
Third. Most engineers in the early days couldnt design a proper write lock circuit that would protect the ram contents during brownouts or powercycles

I might accept these reasons if many existing working designs which used a low power SRAM and battery and write protect circuit were not changed to use NVSRAMs.  In some cases the existing board was not even changed.  I considered altering my 2440 back to the original SRAM plus battery configuration but found a better option.

Quote
For some devices they actually released the sequence to put the device back in freeze mode . Data is lost of course.

The data is also lost even while powered externally if the internal battery voltage drops far enough to disable the supervisory circuits.

I prefer EEPROMs.
 

Offline tpw_rules

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #14 on: May 11, 2014, 06:25:48 pm »
http://www.eevblog.com/files/Prema6047-ROM-8-5-91.BIN

not a firmware (at least the primary one)
all it appears to do is count to fff8 (delay?) and jump to $8035

Code: [Select]
loc_0:                             
                CLD
loc_1:                             
                LDA     #$FF
loc_3:                             
                STA     $0003
                LDA     #$F8 
                STA     $0002
                LDA     #$C1
                STA     $0001
                LDA     #0
                STA     $0000
                LDA     #0
                STA     $0004
                TAY
loc_16:                             
                CLC
                LDA     $0000,Y
                ADC     $0004
                STA     $0004
                INC     $0000
                BNE     loc_23
                INC     $0001
loc_23:                             
                LDA     $0001
                CMP     $0003
                BNE     loc_16
                LDA     $0000
                CMP     $0002
                BNE     loc_16
                LDA     $0004
                STA     $FFF9
                NOP
                JMP     $8035

can test code at http://skilldrick.github.io/easy6502

The 6502 memory map looks vaguely like this (derived from staring at the schematic):
Code: [Select]
$0000-$1FFF (4864 RAM)
 $2000-$3FFF (Dallas RAM; repeated 4 times)
 $4000-$6000 (nothing)
 $6000-$67FF (6520, 6821 equivalent; 4 addresses repeated $200 times)
 $6800-$68FF (68488 GPIB controller; 8 addresses repeated $100 times)
 $7000-$77FF (uPD8279 display/keypad controller; 2 addresses repeated $400)
 $7800-$7FFF (nothing)
 $8000-$FFFF (ROM; the 27C256 Dave has provided)

The 6502 reads the reset vector from $FFFC (little endian), which indicates a start address of $C800. There, in the ROM, you will find more sensible initialization code.

EDIT: I've been looking at the code and considering doing a dis-assembly. Would that be of use to anybody?
« Last Edit: May 11, 2014, 07:01:56 pm by tpw_rules »
 

Online David Hess

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #15 on: May 11, 2014, 06:28:09 pm »
Might it be possible to replace the battery RAM with an EEPROM?

Seems you have not read the entire threat  :=\

Seems you have not tried it. :)

Quote
An EEPROM will not work because it needs waiting time after each write, the software would have to be modified   :scared:

True enough.

Quote
An FRAM will work though, since it is a RAM with EEPROM features. Data retention time 151 years  :-+

FRAMs, or at least the ones I have checked, have different strobe requirements which may preclude using them as a drop-in replacements.

"Users who are modifying existing designs to use F-RAM should examine the memory controller for timing compatibility of address and control pins. Each memory access must be qualified with a LOW transition of CE."

Quote
Here my original post:
Dave might consider to whack in an FRAM as a replacement for the DALLAS ZeroPower NV-SRAM
They are available as 8Kx8 versions, like the 6164 SRAMs in JEDEC standard SOIC chip.
Modify message

I have used Cypress Semiconductor EEPROM based NVSRAMs as drop-in replacements for 64kx8 Dallas NVSRAMs.
 

Offline Chipguy

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #16 on: May 11, 2014, 06:50:28 pm »
Quote

Seems you have not tried it. :)
FRAMs, or at least the ones I have checked, have different strobe requirements which may preclude using them as a drop-in replacements.

I have tried it once replacing a 32KB SRAM in a battery backuped music equipment from the early 90s. It worked great.
The MCU used was a Hitachi 63B05 or something like that IIRC.

But I can see what you are on about. The /CE Signal needs strobing every byte, which, depening on the exact design could be a problem.
So the Interface PCB should include an OR gate and an AND gate to let the /CS signal go low only when either /WE or /RE are low.
This needs of course, that the /RE signal strobes low once every read.


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Offline quarks

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #17 on: May 11, 2014, 07:39:33 pm »
A replacement of a Dallas DS1220 for a 3458A with F-RAM would be very interesting to see, but unfortunately so far I have not
heard of success.
If anyone has details how to make it work, please share.
« Last Edit: May 12, 2014, 06:49:12 am by quarks »
 

Offline Stonent

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #18 on: May 11, 2014, 09:22:19 pm »
There's also this option...



It's a hack but it would work.

Sun workstations used to store their ethernet MAC address in a Dallas chip.  If the battery failed, the computer would still power up but the MAC would be just "FF" repeated.

So you can google Sun NVRAM hack and see all sort of pictures of people taking dremel tools to remove the potting to get inside to solder wires.
« Last Edit: May 11, 2014, 09:24:03 pm by Stonent »
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Offline EEVblog

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #19 on: May 12, 2014, 02:41:29 am »
It's a hack but it would work.

Why would you bother?
You can still buy the DS1220
 

Offline EEVblog

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #20 on: May 12, 2014, 02:42:54 am »
Well, the battery must be really marginal, as you'd expect. I just got an Error 8 on the original NVRAM chip, so that's that. Had to re-install the factory cal values from the ROM.
 

Offline Stonent

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #21 on: May 12, 2014, 02:50:23 am »
It's a hack but it would work.

Why would you bother?
You can still buy the DS1220

Well the people who were doing this are IT guys not electronics guys.  You can set the MAC from the console and if there's power to the chip, it will stick.
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Offline Stonent

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #22 on: May 12, 2014, 02:51:00 am »
Well, the battery must be really marginal, as you'd expect. I just got an Error 8 on the original NVRAM chip, so that's that. Had to re-install the factory cal values from the ROM.

You didn't save the contents of the original Dallas chip?
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Offline SeanB

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #23 on: May 12, 2014, 04:36:41 am »
He probably did. Would be interesting to see the new values in the chip now to compare them.
 

Offline Bored@Work

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Re: EEVblog #615 - Prema 6047 Multimeter Followup
« Reply #24 on: May 12, 2014, 05:28:48 am »
You didn't save the contents of the original Dallas chip?

Hu? The whole video was about doing that.
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