[time-nuts] Frequency Counter Choice

[jimlux]

On 10/22/20 12:08 PM, Oz-in-DFW wrote:
> On 10/22/2020 11:52 AM, jimlux wrote:
>>   I wonder if one could implement the protocol using GPIO pins on
>> something like a Beagleboard or Arduino clone?
>>
>> (yes, as a product, with the right connector and line
>> driver/receivers, etc. - it would cost the same as a Prologix... but
>> as a hack...)
>>
>> After all GPIB is a very old standard, and was developed back in the
>> day of 1 MHz logic. I think you could do the handshaking in software -
>> punch the bits one by one, assert DAV, etc.
>> Listener reads bits one by one, then asserts the ACK or NAK
> Actually it's bytes.  It's byte-serial not bit serial.


Yes, but sometimes you don't have a way to write all the bits of an 8 
bit interface at once, and you have to do them one at a time (if you're 
going through some abstracted interface that only allows individual pins 
to be set - for instance, Arduinos work that way:

digitalWrite(pin#, HIGH)

I think GPIB would still work if you had to do 8 digitalWrite() calls, 
then a final digitalWrite() call to assert DAV.


I suspect that for a number of Arduino type processors, there is a way 
to write or read all 8 at once, assuming you were clever enough to pick 
the right pins to use.



> 
> Most modern micros can pretty easily keep up with the bus - especially
> if you use GPIOs that can generate interrupts. 

I think that since the bus is fully handshaked (handshook?) an 
arbitrarily slow processor can do it, no interrupts required.


The only real challenges
> are finding a reliable source of the appropriate connector - and driving
> the 5V lines at the current levels required for a loaded bus.  Most
> modern micros do not have 5V tolerant I/O but that's pretty easily dealt
> with. Connectors can be had, NORCOMP's 112 series should be ideal.
> https://www.norcomp.net/series/112-series and are available through
> DigiKey, Mouser, Farnell, etc. TI's SN75160/SN75161 bus transceivers
> still seem to be in production as SOICs as well.
> 
> I've noodled about building a board that was intended to connect to a
> single instrument, but not really gotten serious about it.  I wanted
> everything in the shop on Ethernet.


Buy a Prologix - $200 from sparkfun, for instance.

Unless your time is free and you don't have any more interesting 
projects to work on.

I wonder if Prologix makes one that is PoE?  Now that you can get cheap 
switches with PoE injection, that would be attractive.  Getting rid of 
all those wall warts would be nice.



> 
> Oz (in DFW)
> 
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