[ntp:questions] Re: distance to dcf77 transmitter: how to set the fudge?

Alain alainm at pobox.com
Sat Jan 29 02:33:27 UTC 2005


> And you have to add to this the effects of the serial line between your
> reciever and your PC. The cheap recievers sample the erial line with 50
> baud. That is 20 msec between each of the following ||
> 
>    |StartBit|bit 0|1|2|3|4|5|6|7|Parity bit|Stop bit|Stop bit|
>     ^                               The serial interface     ^ sends
>     |                               the data to the PC
>     | The beginning of the start bit is sampled with 16 times
>       the baud rate (or was it 8 times?)

The start bit is sampled at the begining, then confirmed at the middle 
of the start bit. Then every bit is sampled at it's middle. The data 
should be sent to the PC at the middle of the *first* stop bit and the 
second stop bit is ignored. There are hardware bugs that cause the 
second stop bit to be tested but IIRC PCs don't have this bug.

Alain



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