The FT2232 incorporates a command processor called the Multi-Protocol Synchronous Serial Engine (MPSSE). The purpose of the MPSSE command processor is to communicate with devices which use synchronous protocols (such as JTAG or SPI) in an efficient manner. The FT2232's MCU Host Bus Emulation mode also uses the MPSSE technology to make the chip emulate a standard 8048/8051 MCU host bus.
The MPSSE Command Processor unit is controlled using a SETUP command. Various commands are used to clock data out of and into the chip, as well as controlling the other I/O lines. If disabled the MPSSE is held reset and will not have any effect on the rest of the chip. When enabled, it will take its commands and data from the OUT data written to the OUT pipe in the chip. This is done by simply using the normal WRITE command, as if data were being writen to a COM port. Any data read will be passed back in the normal IN pipe. This is done using the normal READ command, as if data were being read from a COM port.