[time-nuts] Trimble Thunderbolt 1pps

[David McGaw]

I pointed out a while ago that the modern chips like the MAX232 have a 
positive receiver threshold so TTL drive is fine for short runs.

73,

David


On 1/27/14 10:35 AM, Javier Herrero wrote:
> 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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