[time-nuts] Can (will) a M12+T generate a negative sawtooth message ?

EWKehren at aol.com EWKehren at aol.com
Sun May 18 20:55:49 EDT 2014


I think there is confusion between where there is a negative delay. Yes the 
 M12 can have a negative value but in order to correct for the full range 
of the  saw tooth at zero the DS chip has to add 128 nsec delay plus the zero 
value.  Depending on the message it ads or subtracts from that value. As 
saw teeth  get smaller there are chips with .25 and .5 nsec. steps. Later GPS 
units  have messages with higher resolution steps.
Bert Kehren
 
 
In a message dated 5/18/2014 8:26:31 P.M. Eastern Daylight Time,  
tvb at leapsecond.com writes:

-128 is  0x80
+127 is 0x7F

If in doubt, just look at the sawtooth correction  messages coming out of 
your M12.

/tvb (i5s)

On May 18, 2014, at  4:17 PM, Chris Albertson <albertson.chris at gmail.com>  
wrote:

>> Chris,
>> 
>> The manual clearly  states -128 to +127. What's your problem with that?
> 
> Yes it  gives that range.  It says the value is stored in 8 bits.
>  
> But how is it stored?  Certainly not as sign bit and 7 bit  magnitude
> or you could not have -128.    They don't say but  options are either
> an assumed bias of -128 or twos complement.   I bet it's an assumed
> bias.
> 
> 
> --  
> 
> Chris Albertson
> Redondo Beach, California
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