Minh Van wrote in a message to All:
 MV> is there a difference between a null modem cable and a serial
 MV> (female-female) cable ? i'm trying to link two PCs together for
 MV> basic file xfers. 
Yes.  In a serial cable, pin 2 at one end connects to pin 2 at the other end, 
pin 3 connects to pin 3 and so forth. In a null modem cable, the data and 
handshaking lines are crossed over -- Tx at one end is crossed to Rx at the 
other, Clear To Send (CTS) is crossed to Request To Send (RTS) and so forth.  
For instance, if you want a 9 pin connector at each end of a null modem 
cable, you'd connect the following lines:
     End A     End B
 Tx  2---------3 Rx
 Rx  3---------2 Tx
 DTR 4---------6 DSR
             |-1 CD
 Gnd 5---------5 Gnd
 DSR 6---------4 DTR
 CD  1-|
 RTS 7---------8 CTS
 CTS 8---------7 RTS
 RI  9         9 RI
The important lines are the Tx/Rx and ground.  In many cases, those three are 
all you need.  Otherwise, you may need to wire up the crossed over handshake 
lines as well.  The ASCII picture above may not make it clear that at each 
end, pins 6 and 1 are wired together and to pin 4 at the far end.
Tx  -- transmit data
Rx  -- receive data
DTR -- Data Terminal Ready
DSR -- Data Set Ready
CTS -- Clear to Send
RTS -- Request to Send
CD  -- Carrier Detect
RI  -- Ring Indicator (very rarely used)
Regards,
       David
--- timEd/2 1.10+
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