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Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)

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joeqsmith:

--- Quote from: m k on February 21, 2021, 11:30:33 am ---
--- Quote from: joeqsmith on February 20, 2021, 11:59:10 pm ---What's the plan now?  Do you have a goal in mind for the old meter?

...

I was wondering more about trying to make sense of the firmware.   If you wanted to add a feature or fix something. 

--- End quote ---

i8080 is a notorious hardware partner.

If you check those I/O example sections of manuals of the era you'll get the idea.
...

--- End quote ---
My question must not have translated very well.  I just didn't understand why anyone would invest the time.  There must be a reason, an end goal.   Maybe it's just to learn some vintage design for the fun of it.  Maybe to improve some aspect. 

SilverSolder:
Understanding vintage tech is always instructive.

One concrete goal might be to understand them better, so they can be kept in useful service for many years to come. There aren't many alternatives in this price range that have comparable specs, especially if you include AC in the comparison - so good examples are worth taking care of.

Another concrete goal might be finding a way to verify and perhaps even calibrate these meters (including aligning the A/D) assisted by a script running on the computer - so you could do it more often, with less calibration equipment (depending on how clever we can get), and thereby enjoy the benefits of having such a good specification meter in the first place - i.e. being able to use it for other electronics projects where measuring stuff very precisely / accurately is beneficial.

Everything depends on what we discover when we look under the hood.   If the code is a super complicated haystack, it won't be easy to do anything with it.  If there is some method to the madness in there, it may be possible to make changes - or it might be possible to leverage the fact that we know what it is doing, to "trick" it into something else.  Time will tell!  :D 

Going completely crazy, in theory, you could even make completely new modules to fit into the motherboard...    a truly crazy person could make a new controller board out of an Arduino, for example...   (I did say truly crazy!)   ;D


SilverSolder:

--- Quote from: m k on February 21, 2021, 11:30:33 am ---
--- Quote from: joeqsmith on February 20, 2021, 11:59:10 pm ---I was wondering more about trying to make sense of the firmware.   If you wanted to add a feature or fix something. 

--- End quote ---


i8080 is a notorious hardware partner.

If you check those I/O example sections of manuals of the era you'll get the idea.
Since the processor is really just that it's doings are expensive and bulky pretty fast.
Means that what ever you do is suppose to be a "custom" chip from Intel, so a rich man poor man game benefiting Intel in every corner.

This Fluke is most complicated I've tried to figure out and it has only one of those support chips, that clock maker.
That, I understand, is also a norm among these things, other hardware makers thought they really don't like that benefiting Intel part.

Outcome was what is seen here, shortage of address and data lines made people inventing all kind of custom chip alternatives.
Lack of speed wasn't a good thing eighter, though pipelining got a head start.

Few examples, 0x4000 is start of RAM and 0x8000 is start of hardware I/O where only upper half of address is inuse.


--- Code: ---        ram:0585 21 0f 40        LXI        HL,0x400f
        ram:0588 86              ADD        (HL)
                             LAB_ram_0589                                    XREF[1]:     ram:058a(j) 
        ram:0589 be              CMP        (HL)
        ram:058a c2 89 05        JNZ        LAB_ram_0589
        ram:058d c9              RET

--- End code ---

0x8e ohms converter
0xa2 display numbers
0xaa parallel control out
0xac parallel D7 -> ?

0xa3 display extras and 0xa2/1 enabler
0xa1 display/keyboard address


--- Code: ---        ram:176a e5              PUSH       HL
        ram:176b 26 ae           MVI        H,0xae
                             LAB_ram_176d                                    XREF[1]:     ram:1770(j) 
        ram:176d 7e              MOV        A,(HL)
        ram:176e e6 04           ANI        0x4
        ram:1770 ca 6d 17        JZ         LAB_ram_176d
        ram:1773 26 a7           MVI        H,0xa7
        ram:1775 71              MOV        (HL),C
        ram:1776 e1              POP        HL
        ram:1777 c9              RET

--- End code ---

I've recently wasted time with google.
Everyting seems to be plently first and then finally just junk.
I tried to find an i8080 emulator that would suite for hardware testing but found nothing.
Memory says that Altavista was better.

Obviously I had to start doing my own emulator, it's still just a shell but I'll upload it if it becomes usefull.
For a moment I thought maybe Ghidra addon can do it but then later there will be an avoidable obstacle anyway.

--- End quote ---


It sounds ambitious to make an emulator!  -  but the 8080 is probably a simple enough CPU that it isn't as crazy as it sounds. 

I also noticed the lack of support chips in this design.  I guess that cost was an issue, and the designers were pretty clever.  They did manage to pack in what needed to be packed in.

Wish we could get hold of the original program listing - that would be cool! 


joeqsmith:
To try to make compare the two meters, I set the HP34401A to 100PLC.  I then collected data for the same length of time it took the Fluke to make the measurement.  I took the mean of that data and used that as the reading.   Basically averaging in software rather than in the meter. 

The Fluke had been running for a few days and was very stable by the time I collected the data.   In the following graph, the white is after the HP had been on for an hour.  Notice how it continued to drift for another 6 hours.     Right after setting up the measurement, it also took the Fluke another hour or so to settle out.   The Red and the Green traces are after both meters had settled.   

joeqsmith:
In this graph I have normalized both data sets to zero.  This represents roughly 15 hours of data for each meter. 

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