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 <jherr...@hvsistemas.es> To: Discussion of precise time and frequency measurement <time-nuts@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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
