The Goyatek I2C I/o Expander is a CMOS I/O Expander device (aka GPIO) that provides 8/16-bit of general purpose parallel input/output expansion for I2C-Bus SMBus applications.

They consist of one or two 8-bit Configuration (input or output selection), Input Port, Output Port and Polarity Inversion (active high or active low operation) registers. At power on, all of I/Os are configured as inputs. The system master can configure the I/Os as either inputs or output by writing to the Configuration bits. The data for each input or output is kept in the corresponding Input or Output register.