Scope
This application note describes a simple interface for keyboard entry to the SA253x family via a Microcontroller. It also includes hardware description , flowchart and a software example based on the 80Cxx - family of Microcontrollers.

Key Features
• only 5 outputs and 1 input required from µC for handshake to access all keys in the SA253x keyboard matrix
• universal interface, not restricted to specific Microcontrollers
• supports both 3V- and 5V- µCs
• same hardware for all single chip telephones : SA2531/2
• same software for all single chip telephones, only key labels must be replaced