Re: [volt-nuts] HP-3458A NVRAM

[Randy Evans]

Actually, it could make a difference depending on when the processor tries
to access the memory on start up.  The Maxim app note mentions that many
legacy programs designed for the DS1220Y may not work with the DS122AD,
hence the reason for the question.  I really would like to hear from
someone that has actually successfully replaced the DS1220Y with the
DS1220AD, since the DS1220Y is no longer avaialble..

On Fri, Nov 10, 2017 at 5:20 AM, Poul-Henning Kamp 
wrote:

> 
> In message  gmail.com>
> , Randy Evans writes:
>
> >Does anyone know if the DS1220AD will work as a direct replacement for
> >the DS1220Y
> >NVRAM chip currently installed in the HP-3458A?  There is a timing
> >difference between the two devices, as explained in Maxim AN 202.
>
> I don't think that difference will make any difference.
>
>
> --
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>
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[volt-nuts] Unable to zero 3420B on 10**5 sensitivity

[David C. Partridge]

The first step of the calibration instructions 5-38 a) ask me to select the
1V range, and x10**5 sensitivity and to zero the meter using the front panel
zero pot.  I couldn't get that to zero.

The next step which was to zero at x1 sensitivity using A4R16 works just
fine.

I checked and replaced the fixed resistors R49, R14 and R15 on the A4 as
they were well out of tolerance (particularly R14 and R15 at 60K and 62K).
This improved things somewhat but the best I can do with the front panel
zero control on the 10**5 setting is a reading of about +0.8 on the meter
which is almost full scale.

There were no obviously out of line DC voltages in the DC portion of the
amp, save that the output at the emitters of Q12/Q13 in this condition was
about 0.78V

Chopper amps are not exactly something I've messed with before now except in
the form of IC opamps and I'm struggling again, so any help will be much
appreciated.

The schematic for the 3420B A4 amplifier board is Figure 7-8 (pp. 7-17/7-18)
which is on page 39 of the Keysight pdf file.

I worked through the troubleshooting tree but that just led me to believe
that the unit is mostly working ...

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Re: [volt-nuts] HP-3458A NVRAM

[Poul-Henning Kamp]

In message 
, Randy Evans writes:

>Does anyone know if the DS1220AD will work as a direct replacement for
>the DS1220Y
>NVRAM chip currently installed in the HP-3458A?  There is a timing
>difference between the two devices, as explained in Maxim AN 202.

I don't think that difference will make any difference.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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[volt-nuts] HP-3458A NVRAM

[Randy Evans]

Does anyone know if the DS1220AD will work as a direct replacement for
the DS1220Y
NVRAM chip currently installed in the HP-3458A?  There is a timing
difference between the two devices, as explained in Maxim AN 202.

"the "Y" parts had a reset timeout on the order of milliseconds while the
"AD"
parts have a timeout of 125ms. When replacing the Y part with the AD part,
it must be determined that
the controlling processor does not become active during a power-up cycle
for at least 125ms to ensure
that the NV SRAM is available before the processor attempts a memory
access."

There have been documented cases where the new DS1220AD part will not work
in circuits designed with the DS1220Y (now discontinued).

I would like to know if anyone has successfully utilized the DS1220AD
before proceeding to buy the parts.  Similar question for the DS1230Y and
DS1230AD.

Thanks,

Randy Evans
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Re: [volt-nuts] Prema 6048 Cal switch confusion

[David C. Partridge]

An aside: The 27C256 EPROMS in these meters are specific to each individual 
meter as they hold the factory calibration constants for that specific meter in 
EPROM (i.e. not generic calibration values).

That's why the sticky labels over the EPROM window have the meter serial number 
written on them as well as the date and model number.

Dave

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of David C. 
Partridge
Sent: 10 November 2017 10:19
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

Just to follow up on this thread ...

I received an M48Z02-150PC1 NVRAM in the post yesterday.

I installed into the meter set to "Cal" and powered on - thus loading default 
constants into it.

I then read this NVRAM and compared to what I had previously read from the 
DS1220Y.  VERY similar with only a few one byte differences here and there, so 
clearly the data in the DS1220Y was valid.

I am amazed that the DS1220Y was still holding its data after 30 years (*three* 
times the advertised life).

Nothing at all like what got loaded into the DS1220AD - clearly that REALLY 
DOESN'T work in these meters.

Given the similarities, I stored what I had previously read from the DS1220Y 
into the M48Z02, and installed that into the meter, and it appears quite happy 
(no checksum failure).

Cheers
Dave
-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of David C. 
Partridge
Sent: 06 November 2017 16:28
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

I just had an email from Prema about this - - long story short: In this 
particular application, the DS1220AD isn't a good replacement for the DS1220Y 
as the timings differ enough to cause a problem.

Prema suggested to use a ST M48Z02-150PC1, so I've ordered one from CPC.

Dave

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of David C. 
Partridge
Sent: 03 November 2017 17:53
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

Randy, That's a very good thought.  I think it is OK in this case as the Error 
8 (checksum fail) occurs about 3 seconds after power on.

If necessary,  I think I could replace the MAX691 supervisory chip with one 
that holds the processor in reset for a bit longer (I think the MAX695 would 
probably be a 100% compatible replacement that holds the processor in reset for 
200mS instead of 50mS after Vcc reaches 4.7V  - PLEASE CORRECT me on this if I 
misread the datasheet).

Dave
 
-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Randy Evans
Sent: 03 November 2017 17:17
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

Dave,

Note the following from Maxim AN 202:

I Replaced My Standard SRAM with an NV SRAM and Now My System Doesn't Work at 
All. What Caused This?

In general, this is caused by one of two things:
First, the designer may not have considered the recovery time, or tREC, of the 
particular NV SRAM selected. On power-up, an internal power monitor disables 
the NV SRAM until a power-good situation and then holds it disabled for an 
additional 2ms (max) or 125ms (max), depending on the NV SRAM Page 5 of 9

after power-good. If the microcontroller attempts to access the memory before 
tREC times out, it will not be able to access the device's memory to read or 
write, so the system fails. Either a software loop on power-up to extend the 
access time past tREC, or moving the NV SRAM access somewhere later in the 
power-on initialization sequence in the microcontroller's firmware will resolve 
the problem. This problem often can be corrected by selecting a CPU supervisor 
that has a reset time longer than the recovery time of the NV SRAM.

Second, selecting the voltage levels at which the NV SRAM and the 
microcontroller become active is critical. If the microcontroller becomes 
active below 4.5V, and the NV SRAM becomes active above 4.75V, the same problem 
of the microcontroller trying to access a disabled NV SRAM occurs. The 
power-good threshold for the two devices should force the system to enable the 
NV SRAM first and then the processor. This involves selecting the NV SRAM with 
the appropriate power-good level and pairing that with a CPU supervisor that 
enables the processor at a higher voltage.

Some NV SRAMs have an active-low RESET output that is synchronous with its own 
internal reset. If this is used to reset the microcontroller, the possibility 
of trying to access a disabled NV SRAM is removed.

and:

Are Any NV SRAMs Not Recommended for Future Designs?

Yes. The DS1220Y and DS1225Y are not recommended for new designs. These older 
devices used a battery reference to determine the power-valid trip-point during 
power cycles. Newer designs use a band gap 

Re: [volt-nuts] Prema 6048 Cal switch confusion

[David C. Partridge]

Just to follow up on this thread ...

I received an M48Z02-150PC1 NVRAM in the post yesterday.

I installed into the meter set to "Cal" and powered on - thus loading default 
constants into it.

I then read this NVRAM and compared to what I had previously read from the 
DS1220Y.  VERY similar with only a few one byte differences here and there, so 
clearly the data in the DS1220Y was valid.

I am amazed that the DS1220Y was still holding its data after 30 years (*three* 
times the advertised life).

Nothing at all like what got loaded into the DS1220AD - clearly that REALLY 
DOESN'T work in these meters.

Given the similarities, I stored what I had previously read from the DS1220Y 
into the M48Z02, and installed that into the meter, and it appears quite happy 
(no checksum failure).

Cheers
Dave
-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of David C. 
Partridge
Sent: 06 November 2017 16:28
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

I just had an email from Prema about this - - long story short: In this 
particular application, the DS1220AD isn't a good replacement for the DS1220Y 
as the timings differ enough to cause a problem.

Prema suggested to use a ST M48Z02-150PC1, so I've ordered one from CPC.

Dave

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of David C. 
Partridge
Sent: 03 November 2017 17:53
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

Randy, That's a very good thought.  I think it is OK in this case as the Error 
8 (checksum fail) occurs about 3 seconds after power on.

If necessary,  I think I could replace the MAX691 supervisory chip with one 
that holds the processor in reset for a bit longer (I think the MAX695 would 
probably be a 100% compatible replacement that holds the processor in reset for 
200mS instead of 50mS after Vcc reaches 4.7V  - PLEASE CORRECT me on this if I 
misread the datasheet).

Dave
 
-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Randy Evans
Sent: 03 November 2017 17:17
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

Dave,

Note the following from Maxim AN 202:

I Replaced My Standard SRAM with an NV SRAM and Now My System Doesn't Work at 
All. What Caused This?

In general, this is caused by one of two things:
First, the designer may not have considered the recovery time, or tREC, of the 
particular NV SRAM selected. On power-up, an internal power monitor disables 
the NV SRAM until a power-good situation and then holds it disabled for an 
additional 2ms (max) or 125ms (max), depending on the NV SRAM Page 5 of 9

after power-good. If the microcontroller attempts to access the memory before 
tREC times out, it will not be able to access the device's memory to read or 
write, so the system fails. Either a software loop on power-up to extend the 
access time past tREC, or moving the NV SRAM access somewhere later in the 
power-on initialization sequence in the microcontroller's firmware will resolve 
the problem. This problem often can be corrected by selecting a CPU supervisor 
that has a reset time longer than the recovery time of the NV SRAM.

Second, selecting the voltage levels at which the NV SRAM and the 
microcontroller become active is critical. If the microcontroller becomes 
active below 4.5V, and the NV SRAM becomes active above 4.75V, the same problem 
of the microcontroller trying to access a disabled NV SRAM occurs. The 
power-good threshold for the two devices should force the system to enable the 
NV SRAM first and then the processor. This involves selecting the NV SRAM with 
the appropriate power-good level and pairing that with a CPU supervisor that 
enables the processor at a higher voltage.

Some NV SRAMs have an active-low RESET output that is synchronous with its own 
internal reset. If this is used to reset the microcontroller, the possibility 
of trying to access a disabled NV SRAM is removed.

and:

Are Any NV SRAMs Not Recommended for Future Designs?

Yes. The DS1220Y and DS1225Y are not recommended for new designs. These older 
devices used a battery reference to determine the power-valid trip-point during 
power cycles. Newer designs use a band gap reference. The battery-referenced 
devices had a trip point that decreased during the life of the device. Devices 
using the band gap have a trip point that is stable for the life of the product.

The DS1220AD and DS1225AD are recommended for new designs needing the 
functionality of a 16kb or 64kb NV SRAM. For existing designs, the DS1220AD or 
DS1225AD may be considered as replacements; however, the "Y" parts had a reset 
timeout on the order of milliseconds while the "AD"
parts have a timeout of 125ms. When replacing the Y part with the AD part, it 
must be determined that the