The 33978 is designed to detect the closing and opening of up to 22 switch contacts. The switch status， either open or closed， is transferred to the microprocessor unit （MCU） through a serial peripheral interface （SPI）。 This SMARTMOS device also features a 24-to-1 analog multiplexer for reading the input channels as analog inputs. The analog selected input signal is buffered and provided on the AMUX output pin for the MCU to read. Independent programmable wetting currents are available as needed for the application. A battery and temperature monitor are included in the IC and available via the AMUX pin. The 33978 device has two modes of operation， Normal and Low Power Mode （LPM）。 Normal mode allows programming of the device and supplies switch contacts with pull-up or pull-down current as it monitors the change of state on the switches. The LPM provides low quiescent current， which makes the 33978 ideal for automotive and industrial products requiring low sleep-state currents.