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TCP-group 1995

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Re: Flag Frames

>  FS> Does anyone out there know if the statement in the NB-96 
>  FS> modem manual is correct about not all tncs sending flag 
>  FS> frames is true ???
> Some TNCs send square wave for sync instead of HDLC flags ahead of a frame. 
> The idea is to allow the receiver to recover the data stream and acquire phase
> lock more quickly.  Sometimes this works, sometimes it messes things up.  All
> TNCs send at least one HDLC flag, even if they do not use flags for sync idle.

In the standard TAPR firmware (starting with v. 1.1.7), the alternating bit
sequence (which is a continuous run of '0' data bits before NRZI encoding)
is sent for the TXDELAY interval.  The number of flags sent after that is
set by the TXDELAYC param, which has a minimum of 1 and defaults to 2.
I suppose most TNC manufacturers have followed suit...


Barry McLarnon    VE3JF/VA3TCP  |  Internet: barry@dgbt.doc.ca
Communications Research Center  |  AMPRnet:  barry@va3tcp.ampr.org
Ottawa, Ontario, Canada         |  FreeNet:  aa187@freenet.carleton.ca

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