n. Transmission of data on a serial line, when
accomplished by rapidly tweaking a single output bit 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
Bit bang was used on certain early models of Prime computers,
presumably when UARTs were too expensive, and on archaic 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.