bit bang

bit bang

   Transmission of data on a {serial line} accomplished by
   rapidly changing a single output bit, in software, at the
   appropriate times.  The technique is a simple loop with eight
   OUT and SHIFT instruction pairs for each byte.  Input is more
   interesting.  And {full-duplex} (doing input and output at the
   same time) is one way to separate the real hackers from the
   {wannabees}.

   Bit bang was used on certain early models of {Prime}
   computers, presumably when {UARTs} were too expensive, and on
   archaic {Zilog Z80} micros with a {Zilog} PIO but no SIO.  In
   an interesting instance of the {cycle of reincarnation}, this
   technique is now (1991) coming back into use on some {RISC}
   architectures because it consumes such an infinitesimal part
   of the processor that it actually makes sense not to have a
   {UART}.

   [{Jargon File}]