Introduction
The STR91xFA EMI bus is a very flexible bus and is user programmable. The bus can be configured to interface to different types of memory devices, including SRAM, Flash memory, ROM or PSRAM. Some of the programmable features of the EMI bus are:

● Multiplexed or non-multiplexed bus
● Bus width: 8 or 16 bit
● Address lines select: A0-15 or A0-A23
● Read and Write signal timing and wait state insertion
● Asynchronous or synchronous bus access
● Page or burst mode access
● Chip select signals (CS0-3)
● ALE polarity and pulse width
● Bus clock (BCLK) frequency

This application note covers the EMI asynchronous mode configuration for interfacing to standard memory devices in Section 1: Interfacing with asynchronous memory.

It covers also EMI Synchronous mode which has a different bus timing and configuration in Section 2: Interfacing with synchronous memory.

Software is available with this application note and can be downloaded separately online from www.st.com.