1.2.2. Functional Description of the Microcontroller I/O Expander

AN 265: Using Altera MAX Series as Microcontroller I/O Expanders

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Date 9/22/2014

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1.2.2. Functional Description of the Microcontroller I/O Expander

The I/O expander operates as a slave that sends and receives data from and to the microcontroller through the MCU port.

Table 3. Operation Modes of the Microcontroller I/O ExpanderDuring read and write operations, set the `MODE` signal control pin to low.
Mode	Description
Read	In read mode, the microcontroller receives the incoming data through the I/O expander. The selected port (A, B, C, or D) becomes an input port and the MCU port becomes an output port. When the `RD` and `CS` signals are low, the application enables the clock through the input data registers. On the rising edge of `CLK`, the I/O expander writes the data from the selected port to the input data registers.
Write	In write mode, the microcontroller transmits data out through the I/O expander. The selected port (A, B, C, or D) becomes an output port and the MCU port becomes an input port. When the `WR` and signals are low, the application enables the clock through the output registers. On the rising edge of the `CLK` signal, the I/O expander writes the data received at the MCU port to the output data register of the selected port.
Disabled	In this mode, the microcontroller cannot receive or transmit data through the I/O expander. When `WR` or `RD` signal is high, the application disables the `CLK` through the I/O data registers.