[volt-nuts] Prema 6048 Cal switch confusion

David C. Partridge david.partridge at perdrix.co.uk
Fri Nov 3 05:54:19 EDT 2017


This gets odder and odder.   I put the new DS1220AD into the burner and read it.   Pretty random rubbish.

So I cleared it to all FF and inserted into the meter set to Cal mode and powered on - it apparently copied the default Cal constants to the NVRAM.

However when I took it out again and looked at the content it didn't look anything like what I'd read from the original NVRAM, and was mostly still x'FF' but with blocks of ten bytes of zeros at x'100' boundaries, followed by zeroes starting at x'6C7' to x'7ef' and what looks like a checksum at x'7f0'.   I can't believe that these are cal constants specific to this meter!  Though they might be a set of default constants for any 6048!

Filling it with all 00 resulted in an Error 8 (Checksum failure).

I then programmed it with the data I had read from the DS1220Y (and had verified).   That also gave an Error 8.

The data I read is attached in Intel Hex format.

I'm wonder whether the meter is failing to read the original NVRAM in a way that somehow passes checksumming????

Dave
-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of Tom Miller
Sent: 02 November 2017 19:05
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion

How about copying the contents of the old nvram to the new one?


----- Original Message ----- 
From: "David C. Partridge" <david.partridge at perdrix.co.uk>
To: "'Discussion of precise voltage measurement'" <volt-nuts at febo.com>
Sent: Thursday, November 02, 2017 2:58 PM
Subject: Re: [volt-nuts] Prema 6048 Cal switch confusion


> Update - when I tried this I was using a brand new DS1220AD-100IND (blank) 
> to replace the DS1220Y.
>
> Reinstalling the DS1220Y and it worked as expected!  Processor must detect 
> cal mode by writing to NVRAM - if succeeds, then in Cal mode??? Maybe
>
> Is there some obscure incompatability between the DS1220AD and the 
> DS1220Y???
>
> Dave
>
> -----Original Message-----
> From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of David C. 
> Partridge
> Sent: 02 November 2017 18:23
> To: 'Discussion of precise voltage measurement'
> Subject: [volt-nuts] Prema 6048 Cal switch confusion
>
> I've got a Perma 6048 that I've trying to put into Cal mode.  It just 
> won't!
>
> The switch on the rear panel works OK, AFAICT when in the Cal position it 
> connects ~WE on the DS1220 (pin 21) and ~W on the $864 SRAM (pin 27) to a
> 4K7 pullup to +5V and to the output of an LS00 which should be strobing 
> the
> Write lines low as needed.   I can't see any way in which the processor 
> can
> be informed of the switch setting!  In measure mode it just connects ~WE 
> on the DS1220 to a 10k pullup to +5V.
>
> The schematic is on page 120 (Figure 11.4) of the user manual and also 
> page
> 9-7 of the service manual.
>
> Clearly I'm missing something - as a friend reports that his does go into 
> cal mode.
>
> Confused ...
> Thanks
> Dave
>
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