Transmission of data on a serial line, when accomplished by rapidly
tweaking 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 {wannabee}s.
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 returned to use in the early 1990s
on some RISC architectures because it consumes such an infinitesimal
part of the processor that it actually makes sense not to have a
UART. Compare {cycle of reincarnation}. Nowadays it's used to
describe I2C, a serial protocol for monitoring motherboard hardware.
[glossary]