MOS Technology SPI
The 6529 Single Port Interface (SPI) was an integrated circuit made by MOS Technology. It served as an I/O controller for the 6502 family of microprocessors, providing a single 8-bit digital bidirectional I/O port. Unlike the more sophisticated 6522 VIA and 6526 CIA, it did not allow the data direction for each I/O line to be separately specified, nor did it support serial I/O or contain any timer capabilities. Because of this, it did not achieve widespread use.