NULL-MODEM CABLES(NMCs):  These cables are needed to connect 2 pieces of Data
 Terminal Equipment(DTE) together.  The NMC became a requirement based on the
 RS232 standard for the DTE interface.  The DTE port expected to be connected
 to a modem(DCE), not another piece of DTE.  Normally a straight-through
 cable was used to connect a computer or printer to a modem.  If a computer
 was to be connected locally to a printer, a cross-over cable was needed.  The
 term, null-modem cable, stemmed from the cable needed when no(null) modems
 were used.  The purpose of the NMC is to satisfy the RS232 signal needs
 for both pieces of DTE.
Four different NMCs are provided with the SCS software package.  The user may
 page through them endlessly.  An important point with each one of these cable
 designs is that they all assume that the RS232 interface standard was adhered
 to by the vendor providing the DTE.  Hence, only pins 1-8, and 20, are used.
 The main goal in each of these NMCs is to allow data transfer and satisfy all
 the signals normally provided by a modem.  SCS provides these cable designs
 as well as NMCs for ports that don't use all of the leads from the standard.
Another important point is that these NMCs only work in an asynchronous
 environment.  If two pieces of synchronous equipment are to be connected, such
 as in a 3270 environment, timing is an issue.  Unless one of the devices can
 provide this timing(usually pin 24), a null-modem cable cannot be built.  This
 pin is usually connected to pins 15 & 17, which are straight-through. 

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