The switch matrix is ​​a functional module that can be flexibly configured by internal paths. The signals of each peripheral function of the MCU can be used as the entrance of the switch matrix, and each of the multiplexed I/O ports is the corresponding exit, and can be specified by the corresponding register configuration. Peripheral functions are flexibly assigned to the required pins. In the LPC8xx series, it can be distributed through the switch matrix: three-way serial USART0/1/3, two SPI0/1, multiple input and output of SCT timer, two I2C1/2, ADC module, analog comparison ACMP output, clock frequency output CLKOUT and GPIO interrupt output.

The switch matrix connects all of the internal signals listed in the moveable function table to the external pins on the package through the pin assignment registers, or vice versa. The signal inputs required by the internal modules are assigned to the individual pins. The external pin is identified by its default GPIO pin number, PIO0_n. Follow the steps below to connect the internal signal to an external pin:

● Enable the switch matrix clock and the peripheral function clock that needs to be turned on;

● Find the peripheral functions of the desired operation in the movable function table;

● Find the LPC8xx data sheet to determine which pin connection pin function of the LPC8xx package;

● Use the pin description table to find the default GPIO function PIO0_n assigned to package pin x. x is the pin number;

● Find the pin assignment register for the corresponding function in the switch matrix register description;

● Disable any special function of this pin PIO0_n in the PINENABLE0 register. Because some special functions are assigned to specific pins by default, such as external crystal input, the function conflict can be prevented after being turned off.

● Pin number n is programmed into the bit assigned to the pin function. The pin function is now connected to pin x on the package.

Change pin function assignment