[time-nuts] STEL 1175 vice 1173

Magnus Danielson magnus at rubidium.dyndns.org
Wed May 14 18:58:02 UTC 2014

Hi Ed,

Reverse-engineering it would be fun. It's not that much code.

Anyone got a EPROM dump lying around? :)

But regardless, just doing reverse engineering is not enough, one needs 
to adjust frequency programming and possibly adjust some other parameters.

Reverse-engineering as such would be educational.


On 05/14/2014 08:11 PM, Ed Palmer wrote:
> Hi Magnus,
> Yeah, I like a challenge, but let's keep things reasonable! :)  The
> package conversion is easy to accomplish, the FPGA would be a real
> stretch for me, but reverse engineering the system code is more than I
> want to tackle - although I have thought about it!
> Ed
> On 5/14/2014 11:17 AM, Magnus Danielson wrote:
>> Hi Ed,
>> You could probably use a 32 bit DDS, but there will be a whole bunch
>> of little trimmings you would have to do in the CPU code which would
>> require quite a bit of (interesting) work. I would say it would be
>> beyond the scope of most folks.
>> Cheers,
>> Magnus
>> On 05/14/2014 06:53 PM, Ed Palmer wrote:
>>> Hi Corby,
>>> Thanks very much for the offer, but it looks like it would still be a
>>> big project to use an '1175 to replace an '1173.  I think I'll have to
>>> pass.
>>> The package difference (PLCC68 vs. PLCC44) would still require a
>>> daughterboard of some sort.  I've learned a little over the past week
>>> about NCOs and, if I'm right, reducing the clock speed from 45 MHz to 30
>>> MHz would partially compensate for the 32 vs. 48 bit difference.  The
>>> output frequency would be correct, but the waveform would have more
>>> harmonics.  Since the clock is derived from a 90 MHz signal, the
>>> reduction would be easy.  Whether that would have an adverse impact on
>>> the operation of the Datum 4065A is way beyond me.  It looks like both
>>> chips have a 12 bit output which is nice. The '1175 has more features
>>> than the '1173.  I'd have to study the data sheet to see if they can be
>>> configured to make the '1175 act like an '1173.
>>> For now, the plan is to try and source the '1173 in the 48-pin DIP
>>> package and do a (relatively) simple daughterboard to adapt the
>>> packages.  Even that will probably end up costing ~$150.  If that
>>> doesn't work out, there's the possibility of an FPGA replacement. That
>>> would likely allow replacing the AD9713 D/A converter as well as the
>>> STEL-1173.  It turns out that an NCO is a standard application in the
>>> FPGA world.
>>> Ed
>>> On 5/14/2014 9:13 AM, cdelect at juno.com wrote:
>>>> Hi,
>>>> I found two PLCC STEL 1175 in a rack mounted synthesizer I have.
>>>> I'd be willing to sell the chips.
>>>> Would they work?
>>>> Cheers,
>>>> Corby
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