[time-nuts] Trimble Thunderbolt 1pps

[Robert Atkinson]

Hi Javier,
Our posts crossed. However the 1489 has a positive threshold (they call it turn off threshold) of 0.75 to 1.25V. They can be shifted to a negative trigger range using the response control pin but this is just a voltage divider and offset voltage, you still only get hysteresis of 1.1V for the "A" version. 
Interestingly the dataheet you linked to says the RS232D spec has a +/-3V threshold (6V hysteresis). I must have missed this or read a different version. I've still not seen a packaged receiver that meets this specification.

Reobert G8RPI.




________________________________
 From: Javier Herrero <jherrero at hvsistemas.es>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Monday, 27 January 2014, 15:35
Subject: Re: [time-nuts] Trimble Thunderbolt 1pps
 

On 27.01.2014 15:08, Attila Kinali wrote:
>> In practice, the receiver chip only has one power supply.  It would take
>> extra work to make the switching threshold below ground.
> That's not correct. Standard transceiver chips (like the MAX232 family)
> have an integrated charge pump to get a negative power supply.
>
Hello,

The venerable MC1489 does not need a negative supply, and can have a 
threshold below ground, without too much complication. 
http://www.onsemi.com/pub_link/Collateral/MC1489-D.PDF (the receiver 
circuit diagram is shown)

On the other side, the MAX232 has positive thresholds in the receiver 
side http://datasheets.maximintegrated.com/en/ds/MAX220-MAX249.pdf pag. 6

Regards,

Javier


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