Freescale offers multiple Switch Detection Interface Devices. The 33975 Multiple Switch Detection Interface with Suppressed Wake-Up 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). The device also features a 22-to-1 analog multiplexer for reading inputs as analog.
The 33975 device has two modes of operation, Normal and Sleep. Normal mode allows programming of the device and supplies switch contacts with pull-up or pull-down current as it monitors switch change of state. The Sleep mode provides low quiescent current, which makes the 33975 ideal for automotive and industrial products requiring low sleep state currents.
Improvements are a programmable interrupt timer for Sleep mode that can be disabled, switch detection currents of 32 mA and 4.0 mA for switch-to-ground inputs, and an interrupt bit that can be reset.

FEATUREs
• Designed to Operate 5.5 V ≤ VPWR ≤ 28 V
• Switch Input Voltage Range -14 V to VPWR
• Interfaces Directly to Microprocessor Using 3.3 V/5.0 V SPI
   Protocol
• Selectable Wake-Up on Change of State
• Selectable Wetting Current (32 mA or 4.0 mA for switch-to-ground
   inputs)
• 8 Programmable Inputs (Switches to Battery or Ground)
• 14 Switch-to-Ground Inputs
• VPWR Standby Current 100 µA Typical, VDD Standby Current 20 µA Typical
• Pb-free 32-terminal suffix EK