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Re: FT847 Null Modem



>John Johnson wrote:
>
>> Could someone explain what a "null modem" RS232 cable is when (9 pin)
>> compared to a straight cable...the info is needed for my FT 847..
>> Thanks,  I apologize if you receive two versions of this question.
>> 73   fer   now            John   KF7LF
>
>John-
>
>The pin connections you received tell you what to do, but it might help
>to have a word description to put meaning to the answer.  The concerned
>pins are labelled "Request to Send" and "Clear to Send".  By
>criss-crossing the connections, the cable always says, "I'm ready" and
>does so in both directions.


The pinouts I have on the DB-9 female socket and male jack are:

DCD  1
RxD   2  = receive data
TxD   3 = transmit data
DTR  4
Gnd   5
DSR  6
RTS  7 = request to send
CTS  8 = clear to send
Ring  9

Others have described a null-modem cable for DB-9 connectors as crossing
the wires for pins two and three.  This suggests to me that the transmitted
data from the sending Data Terminal is being fed to the receive data pinof
the receiving Data Terminal. 

Otherwise. a Data Set (e.g., a modem) would be required at each end to
perform the swap, as well as other modem-specific functions.   A  regular
modem cable (with pins 2 and 3 being fed straight through)  would be
required in this case.

73, Dick


Richard A. "Dick" Rucker
City of Fairfax, VA
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